China has made strides in building a new stealth fighter jet and Washington is also concerned about a new ballistic missile that could theoretically explode an aircraft carrier nearly 2,000 miles (3,200 kilometres) out to sea. China has also apparently beaten US estimates to develop that weapon.

Gates arrived in Beijing today for talks about these weapons and other military issues with Chinese leaders.

"They [China] clearly have potential to put some of our capabilities at risk," Gates told reporters traveling with him to Asia. "We have to pay attention to them, we have to respond appropriately with our own programs." The US has long known that China wanted to field a stealth jet, but development outpaced US intelligence estimates, Gates said.

China is still years behind US capabilities in radar-evading aircraft, and even by 2015 the US would still have far more flying than any other nation in the world, Gates said.

China says it does not pose a threat and its military forces are purely for defence, which in its definition includes deterring Taiwan, a self-governing island that Beijing claims as its territory, from declaring formal independence.

In an apparent nod to US calls for more openness, China allowed video and pictures of last week's runway tests of its prototype stealth fighter to be taken and posted online.

Gates is trying to coax Chinese military leaders into more regular discussions with the US.

The Pentagon is focusing scarcer defence dollars on ways to counter the kinds of weapons China is now building. Gates said recently he wants to spend more on a new long-range nuclear bomber and updated electronics gear for the Navy that could throw an incoming missile off course.

He will also visit South Korea for talks about averting war with the North, as well as Japan, which is alarmed by Chinese military moves.

The invitation to visit Beijing was a coup for Gates, who invited a Chinese counterpart for similar talks and a visit to the US nuclear weapons headquarters in 2009.