Japan on Saturday expressed concern over what it called a lack of transparency in China's massive defence spending, saying the secrecy posed a "threat" to Tokyo.

China's military budget jumped 11.2 percent year on year to $106 billion in 2012, a rise that has caused unease around the region and especially in Tokyo, Japan's Parliamentary Senior Vice-Minister of Defense Shu Watanabe said.

"There is expansion of the military budget and that is not transparent," he told defence chiefs and senior officials attending an Asia security summit, the Shangri-La Dialogue, in Singapore.

Because of the lack of transparency, Japan is in the dark about the details of China's military spending, he said.

"Chinese military budget growth, what sort of capacities they are trying to expand and what sort of purposes they have are not transparent and in that sense it is a threat," Watanabe added.

He said the unease generated by the issue contrasted with generally positive cultural and economic relations Tokyo has with Beijing.

"On the military front there are some concerns. I think all countries are the same on that front," he said.

China's growing military presence and assertive stance, especially in the South China Sea, where it has overlapping territorial claims with other Asian nations, have rattled nerves in the region as well as in Washington.

US Senator John McCain said in a press conference on the sidelines of the summit that China should be more open about its defence spending.

"What I would like to see is much more transparency on the part of the Chinese government as to how much money is being spent, what it's being spent on and what their overall strategy should be," he said.

"I don't view that China's military buildup is necessarily directed at the United States of America but I do worry when we don't know exactly how much money is spent, what it's on and we would also like to hear what their doctrine will be."

Addressing the conference, Indian Defence Minister A.K. Antony said New Delhi was also concerned about China's military spending.

"Even though we don't believe in an arms race, since China has increased their military capabilities and spending more on defence, in our own way, to protect our national interest, we are also strengthening our capabilities in our borders," he said.