China has contingency plans to dispatch troops into North Korea and secure nuclear weapons in the event of instability in the hardline communist state, according to US experts who have talked to Chinese military researchers.

Any intervention by Beijing would be done as far as possible after consultations with the United Nations, but unilateral action was not ruled out, the experts said in a report published on the websites of two US think tanks.

"If deemed necessary, PLA troops would be dispatched into North Korea," the report said, referring to the Chinese People's Liberation Army (PLA).

"China's strong preference is to receive formal authorization and coordinate closely with the UN in such an endeavor," it said.

"However, if the international community did not react in a timely manner as the internal order in North Korea deteriorated rapidly, China would seek to take the initiative in restoring stability."

The report was compiled by experts from the Center for Strategic and International Studies and the US Institute of Peace - which published the report - and Asia Foundation following their visit to China in June last year.

A spokeswoman for China's foreign ministry on Tuesday said she was unaware of any Chinese strategy to send troops into North Korea to secure nuclear weapons, but did not outright deny that such a plan existed.

"I have never heard of nor seen the so-called plan mentioned in the report," spokeswoman Jiang Yu told reporters in Beijing, without commenting further.

North Korea, which reportedly has up to 10 nuclear bombs, is involved in a de-nuclearization program in return for energy aid and diplomatic and security guarantees under a six-party mechanism involving also the United States, China, Russia, South Korea and Japan.

The program hit a snag recently after Washington accused Pyongyang of not meeting a December 31 deadline for a full declaration of its nuclear programs.

"According to PLA researchers, contingency plans are in place for the PLA to perform three possible missions" in North Korea - humanitarian and peacekeeping missions and "environmental control" measures, the report said.

The measures are intended "to clean up nuclear contamination resulting from a strike on North Korean nuclear facilities" near the Sino-North Korean border and "to secure nuclear weapons and fissile materials."

The report - entitled "Keeping An Eye On An Unruly Neighbor: Chinese views of economic reform and stability in North Korea" - said that in the event of instability in North Korea, China's main priority would be to prevent a flood of refugees.