John C. Liu, the New York City comptroller, has vaulted into the top tier of political figures in the city, building a formidable fund-raising machine that has quickly established him as a contender to succeed Mayor Michael R. Bloomberg.

Mr. Liu recently announced, with great fanfare, that he had taken in $1 million in the first six months of the year, much of it from donors who gave him $800 — to reflect the number 8, which is lucky in Chinese culture.

But there is much about Mr. Liu’s campaign money that does not add up.

Canvassing by The New York Times of nearly 100 homes and workplaces of donors listed on Mr. Liu’s campaign finance reports raises questions about the source and legitimacy of some donations, as well as whether some of the donors even exist. Some two dozen irregularities were uncovered, including instances in which people listed as having given to Mr. Liu say they never gave, say a boss or other Liu supporter gave for them, or could not be found altogether.

Two people who described attending banquets in which Mr. Liu appeared and posed for photos said that company executives who support him provided donations in the names of those in attendance.

In addition, Mr. Liu is not complying with some basic campaign finance laws: To protect against so-called straw donors, the city requires that donor cards submitted with campaign contributions be filled out only by the person making the donation. In numerous instances in Mr. Liu’s campaign, one person appears to have filled out cards for multiple donors.

His campaign is also engaging in bundling, in which well-connected individuals collect contributions for a candidate from friends, relatives and others, but Mr. Liu has not disclosed the bundlers’ names, as required.

Asked about the findings, Mr. Liu, 44, a Democrat, expressed bafflement and vowed to conduct an internal investigation.

“To the extent that there are problems — and I’m not suggesting there are — we cannot accept those contributions, nor do we need them,” Mr. Liu said.

The veracity of Mr. Liu’s donor list has implications beyond his campaign. In New York City, which has a generous campaign finance system, candidates can receive $6 in public money for every $1 raised from individual donors.

Many of the irregularities in Mr. Liu’s campaign account are tied to companies in the Chinese business community in Queens, where he has been hailed as a hero and his picture adorns the walls of shops and restaurants.

One of his most visible sources of support is Dynasty Stainless Steel in Maspeth, Queens, a city contractor that makes metal doors and guardrails for public housing and other agencies. Campaign finance documents show that Dynasty’s president, Ming Kun Lee, and eight people listed as Dynasty workers each gave Mr. Liu $800 in January.

All the donor cards bear the same handwriting, suggesting they were filled out by one person.

Of the eight people listed, however, at least four do not work for the company, according to interviews with them or their relatives. Two of the four told The Times that they never gave to Liu; two others were out of the country. A fifth, a scientist at Columbia University, declined to answer questions.

Raymond Chen, in Flushing, who was listed as a Dynasty project manager who gave $800, said he did not work for Dynasty and did not give to Mr. Liu’s campaign. Mr. Chen, a Pace University student, said he could not afford to contribute to political campaigns, though he may consider doing so in the future.

“Small amounts, yeah, probably,” he said. “Not like a few hundred dollars.”

Dynasty’s president, Mr. Lee, did not reply to e-mails and phone calls seeking comment.

In another case, 18 employees, from janitor to clerk to project manager, for W&L Construction in Fresh Meadows, Queens, were listed as having given $800 apiece to Mr. Liu.

More than half of the donor cards appeared to be filled out by the same hand.

Among them was Zhong Qun Tan of Gravesend, Brooklyn, who is listed as a carpenter. But, in an interview, Ms. Tan said she worked at a garment factory and had never heard of W&L. She said that her husband, a livery driver, had talked to her about donating to Mr. Liu but that she did not know if someone had given money in her name.

Five W&L employees reported their home address as the residence of the company’s owner, Meng Jia Wang. Mr. Wang initially said that the donors were his employees and subcontractors who had attended a fund-raising event for Mr. Liu and that he had permitted them to list his address because their English was not good. When The Times sought contact information to speak to the donors, Mr. Wang referred a reporter to Xing Mei Ni, a secretary at the company.

Ms. Ni said she did not recognize some of the names and declined to provide contact information for those she did. She offered a different account from Mr. Wang’s, saying that there was no fund-raising event, but that the employees decided together, over lunch one day, to make out checks to the Liu campaign, and sent it in one package.

“It was easier for all of us to do the paperwork together,” she said.

Yet another version of events was offered by Kui Ping Young of Flushing, who was described in the campaign finance report as an office worker for W&L who gave $800. In interviews, she and her husband, Andy, said she worked not for W&L but at a nail salon. She said that she was not politically active but that she had bought a ticket for a Liu fund-raising event after her brother, whom she described as a partner at W&L, asked her to.

But she said she spent only $200 on the ticket — not the $800 she is listed as having donated. “Her brother paid for it,” her husband said. “I don’t know anything about the amount. Please go interview somebody else.”

Then there is the case of a construction company called Kang Kang: 10 people are listed on the Liu campaign finance report as a “worker” for Kang Kang, each having given $800 in early May. All of the workers list the company’s business address as 135-25 167 Street in Flushing, but that address does not exist. At the home addresses listed for three of the workers, there is no one there by that name, according to public records and neighbors.

The Kang Kang donor cards all appear to have been filled out by one person.

And one of the workers listed, Sheng Lin Zhang of Elmhurst, Queens, provided an account of how donations were made to Mr. Liu’s campaign. He described attending a recent fund-raising party for Mr. Liu. He said the comptroller appeared at the event, shook hands and posed for photos. While campaign finance records say that Mr. Zhang donated $800 to the Liu campaign, he said that his boss, whose name he gave as Jian Kang Chen, did.

“My boss took care of all that,” he said. “I heard that it was 800 or 900 dollars.”

In a follow-up interview, Mr. Zhang said that the boss had made donations on behalf of some other workers who attended, and would, in some cases, later garnish their wages.

The company itself is hard to locate. The address on the campaign records does not exist, and another address for the company that The Times found through independent research is a residential house. The man listed as its owner did not know anything about Kang Kang.

Mr. Zhang said that he had never visited the company’s premises, and that he and other workers typically met at sites where they worked.

The problems are occurring against a backdrop of an aggressive fund-raising drive by Mr. Liu, the first person of Chinese descent to hold major elective office in New York City.

But with that success have come questions about how he has amassed his war chest. The Times began reviewing his campaign finance records after his most recent filing in July.

In response to the inquiry from The Times, Mr. Liu furnished copies of checks and donor cards for those listed on his campaign finance report. But some of the records raised more questions. Mr. Liu said he had a check for $800 written by Cheng Tsung Tung of Oakland Gardens, Queens, who was listed as a project manager for Dynasty Stainless Steel.

But in an interview, Mr. Tung said that he did not give Mr. Liu’s campaign a check and that he did not work for Dynasty; he owns a gift store.

Mr. Liu, in reviewing his records, acknowledged that donor cards appeared to have been filled out by people other than the purported donors, and said his campaign should not tolerate that.

“It’s got to be your own money,” he said.

In the interview, Mr. Liu vowed to return any money from questionable sources and said he had personally warned many of his donors that they were not helping him if they broke the rules.

As for his failure to list bundlers collecting money for him, Mr. Liu said he would begin complying with the city’s rules.

He also questioned how The Times approached people whose names were on the donor list, many of whom do not speak English well. He suggested that perhaps they were intimidated by the experience, and may have denied donating when they actually did. Many of the interviews were conducted in Mandarin.

“If someone was asking me the question, I’d say, ‘No, no, no, no — I don’t know who you are,’ ” Mr. Liu said.

Mr. Liu’s campaign records suggest he is attracting an unusually large number of new donors to politics; more than half of his 2,100 donors had never given before to any candidate.

A spokesman for the city’s Campaign Finance Board, while declining to comment directly on Mr. Liu’s situation, said that before the city released public money to a campaign, it sought to ensure that donors were being reported accurately.

“If our routine audit reveals documents or contribution patterns that raise further questions, we may conduct a more intensive investigation,” said the spokesman, Eric Friedman.

Mr. Liu began his political ascent in 2002 when he became the first Asian member of the City Council, representing Flushing. He coasted to re-election in 2003 and 2005, then ran for the comptroller’s office in 2009 and won.

Since then, Mr. Liu has emerged as a significant force in city politics, known for his fiery speeches, aggressive courtship of labor unions and blunt criticism of Mr. Bloomberg.

Mr. Liu said that his campaign had never heavily relied on an accountant or treasurer to handle its finances, and that he oversaw much of the operation.

“I’m responsible for my own campaign,” he said. “To the extent that I think something has been done wrong, or people engaged in behavior that broke my rules, we’ll reverse anything.”