Beijing: China is carrying out "routine" military drills on its border with North Korea to maintain combat readiness, China's Ministry of Defence says.

The statement was issued after reports from the United States that Chinese bombers were on high alert with "unusual levels" of activity.

There are renewed fears that North Korea could conduct a nuclear test on April 25, the 85th anniversary of the founding of its military. Last week the Chinese Ministry of Defence denied reports that it would mobilise 150,000 troops to the border, including medical teams, in preparation for any nuclear test by North Korea.

People's Daily, the Chinese government's official mouthpiece newspaper, said on Friday evening that reports that Chinese bombers were on high alert had been denied by the ministry of defence. But it also reported the Ministry of Defence had said it was carrying out a military drill on the border, timed with concern North Korea was preparing for its sixth nuclear test.