China on Wednesday extended its spending spree on the world's largest armed forces, unveiling a 12.2 percent increase in the 2014 defence budget and provoking fresh concern in rival Japan.

Beijing has for years been raising spending on the People's Liberation Army (PLA) in double-digit steps, reflecting its military ambitions as it asserts its new-found economic might and its claims in a series of territorial disputes with Tokyo and others.

The spending has raised eyebrows in the region and Washington.

"We will resolutely safeguard China's sovereignty, security and development interests," Premier Li Keqiang said at the opening of the Communist Party-controlled National People's Congress (NPC).

Beijing will "place war preparations on a regular footing" and "build China into a maritime power", he added.

"We will safeguard the victory of World War II and the post-war international order, and will not allow anyone to reverse the course of history," Li said -- a phrase China often uses in relation to Japan.

China has been expanding its bluewater capabilities in recent years, with its first aircraft carrier going into service in September 2012.

Beijing and Tokyo's vessels and aircraft regularly shadow each other near disputed East China Sea islands called Diaoyu in Chinese and Senkaku in Japanese, raising fears of a clash.

A budget report prepared for the NPC meeting said that "the appropriation for national defence is 808.23 billion yuan ($132 billion), up 12.2 percent".

Shortly after the announcement Japan expressed concern about Beijing's openness about the PLA -- which includes the army, navy and air force.

"The transparency of China's defence policy and military capacity, or lack thereof, has become a matter of concern for the international community, including Japan," Chief Cabinet Secretary Yoshihide Suga told reporters.

This year's stated increase follows rises of 10.7 percent in 2013, 11.2 percent in 2012 and 12.7 percent in 2011.

Analysts believe China's actual military spending is significantly higher than publicised, with the Pentagon estimating it at between $135 billion and $215 billion in 2012.

The United States itself remains far ahead as the global leader in defence spending, with Washington approving a 2014 budget of $633 billion in December.

- Great power ambitions -

China devotes about three times as much as India to defence, and more than neighbours Japan, South Korea, Taiwan and Vietnam combined.

Beijing's spending could match that of Washington by the 2030s, the International Institute for Strategic Studies said in February, but added that its capabilities, expertise and ability to project power would require several more years to catch up.

Nonetheless the increases have raised concern in the US and Asia, particularly in Japan.

In comments ahead of the NPC, the gathering's spokeswoman Fu Ying sought to play down such worries.

"Certain countries have been selling the idea of China as a major threat," she said. "Based on our history and experience, we believe that peace can only be maintained by strength."

China's actions will both fuel the worries of its neighbours and encourage them to strengthen security cooperation with each other and the US, said Denny Roy, an expert on China's military at the East-West Center in Hawaii.

"This would add to the momentum of something that's already in motion," he told AFP.

In December, the cabinet of Japan's hawkish Prime Minister Shinzo Abe agreed to spend 24.7 trillion yen ($240 billion) between 2014 and 2019 in a strategic military shift towards areas of the country facing China -- a five percent boost to the defence budget over five years.

Beijing decried Tokyo's increase at the time as an issue of "great concern to neighbouring countries in Asia and the international community".

China's drive to modernise its military stems from an overall ambition to enhance its global stature rather than disputes with neighbours, Roy said.

Strengthening its maritime forces was important for projecting power further afield, he pointed out.

Following delivery of the Liaoning carrier, he said, China was eager to build up carrier battle groups, and eventually to be able to secure its oil supplies from the Middle East if necessary.

"China would be doing much of its modernising and building as it is now anyway," Roy said. "I think fundamentally it's (about) China's commitment to attaining great power status."

That meant having "a strong military commensurate with China's status in other areas -- its size, its wealth, political influence, cultural influence".