An unconventional project by US university students has concluded that China's nuclear arsenal could be many times larger than current estimates, drawing the attention of Pentagon analysts.

The Washington Post reported Tuesday that Georgetown University students under the instruction of a former Pentagon official have assembled the largest body of public knowledge yet about a vast network of secret tunnels dug by China's secretive Second Artillery Corps, responsible for nuclear warheads.

The 363-page study has not yet been published, but has already sparked a congressional hearing and been circulated among top US defense officials, including the Air Force vice chief of staff, the Post reported.

"Its not quite a bombshell, but those thoughts and estimates are being checked against what people think they know based on classified information," it quoted an unnamed Defense Department strategist as saying.

The newspaper said critics of the report had questioned the students methods, which included using Internet-based sources like Google Earth, blogs, military journals and even a fictionalized Chinese TV show.

But the Post also said the students were able to obtain a 400-page manual produced by the Second Artillery and usually only available to Chinese military personnel.

The students professor, Phillip Karber, 65, spent the Cold War as a top strategist reporting directly to the secretary of defense and the chairman of the Joint Chiefs of Staff, the Post said.

Karber said that -- based on the study of the tunnels -- China could have up to 3,000 nuclear warheads, far higher than the current estimates, which range from 80 to 400, according to the Post.

US officials could not immediately be reached to comment on the report.