Arms control experts are dismissing a report by US university students that suggests China's nuclear arsenal may be much larger than previously estimated, saying the research is shoddy and unreliable.

The unconventional study by students at Georgetown University, under the supervision of a former Pentagon official, examines China's vast network of tunnels for storing missiles and concludes the country could have up to 3,000 nuclear warheads, far higher than the current estimates of roughly 250.

The 363-page study has not been published but it has been circulated at the Pentagon and a Washington Post article Wednesday revealed its findings, which attracted global media attention.

But experts who track nuclear weapons and China's arsenal in particular slammed the report's methods, and a Pentagon official said there were no plans to alter the US government's estimate of China's arsenal.

"China has not produced enough fissile material to produce 3,000 nuclear weapons," said Hans Kristensen, director of the nuclear information project at the Federation of American Scientists.

"Nor do they have delivery systems for so many weapons. It's just inaccurate on all fronts, that estimate," he told AFP.

The report has been reviewed by the Defense Department but has not led to a revision of estimates on the size of China's nuclear force, said a senior defense official, who spoke on condition of anonymity.

"The findings of the report have been noted," said the official. But "there is no change in our assessment."

The study, which was overseen by Professor Phillip Karber, who held senior posts at the Pentagon, combed through Internet-based sources such as Google Earth, blogs and military journals.

Its sources range from a fictionalized Chinese TV show to a 400-page manual produced by the Second Artillery Corps, which oversees China's strategic weapons, according to the Post.

Kristensen and other experts said the report's suggestion that China could have a massive arsenal of thousands of warheads is based on outdated and dubious sources.

"You cannot extrapolate from old data," he said.

Gregory Kulacki, a senior analyst at the Union of Concerned Scientists who follows China's strategic and space programs, said the report's assertions on the size of Beijing's nuclear force were based mainly on Chinese blog posts.

He charged the report failed to cite the original source of the larger estimate, which he alleged is an article published in a Hong Kong magazine -- not an official Chinese government document as Karber maintains.

"This is not competent scholarship." Kulacki wrote Thursday on the Union of Concerned Scientists' website.

"Worse still, neither Karber, nor his students, took the time to find and evaluate the original source of this claim, which is an article published in a Hong Kong magazine called 'The Trend.'"

Jeffrey Lewis of the Center for Non-proliferation studies at Middlebury College, has previously dismissed speculation that Beijing could have thousands of warheads, citing declassified US estimates of Chinese nuclear material.

The Georgetown report also attempts to shed light on China's secret network of underground tunnels, and includes images and accounts of a "missile train" and disguised passenger rail cars to move Chinas long-range missiles, according to the Post.

Kristensen said China's underground network dates back to the 1950s and that it is no secret the country has sought to safeguard its arsenal from attack.

"That's something countries do and China does it too," he said.

He added that the report had "some really serious problems with satellite interpretation."

As an example, Kristensen pointed to the report's description of an alleged deployment site for a new ballistic missile in southern China.

"It's not a missile base at all. It looks to be a cluster of storage facilities for military ammunition," he said.

A large network of underground facilities would be in keeping with China's relatively small nuclear force, as Beijing would want to ensure its warheads survived an initial attack, he said.

A Pentagon report to Congress this year noted China had possibly 5,000 kilometers (3,000 miles) of tunnels and said occasional disclosures of information about the underground network could be a way for Beijing to "send signals on the credibility of its limited nuclear arsenal."

Karber, the Georgetown professor, maintains that the report is a success because it has sparked debate about the size of China's nuclear force.

"I dont have the slightest idea how many nuclear weapons China really has, but neither does anyone else in the arms control community," Karber told the Post. "Thats the problem with China -- no one really knows except them."