China unveiled a fresh double-digit spending boost for its military on Thursday with a 10.1 percent increase in 2015, as it is embroiled in a series of territorial disputes with its neighbours.

Beijing plans to raise its military spending to 886.9 billion yuan ($141.4 billion), according to a budget report to the annual session of the National People's Congress (NPC), the communist-controlled legislature.

The figure is a five year low, but China has for years been raising spending on the People's Liberation Army (PLA) in double-digit steps, flexing its military and economic might as it asserts its claims in a series of rows with Japan and others.

This year's increase comes after a 12.2 percent stated rise last year, and is the lowest since 2010's 7.5 percent, official data show.

But analysts believe spending is significantly higher than publicised, with the Pentagon estimating it at between $135 billion and $215 billion in 2012, and Tokyo called Thursday for "increased transparency" on China's military.

"This may be the lowest increase for five years, but it is pretty much in line with the kind of increases they have had in the last 20," said Richard Bitzinger, senior fellow at the S. Rajaratnam School of International Studies at Singapore's Nanyang Technological University.

"On average they have been about 12 or 13 percent," he added, "and I don't see any kind of slowing down in this for at least another 10 years."

In his speech opening the NPC, Premier Li Keqiang said that "building a solid national defence and strong armed forces is fundamental to safeguarding China's sovereignty".

Beijing will "resolutely safeguard China's maritime rights and interests" and "move closer to achieving the goal of building China into a maritime power", he told delegates in the Great Hall of the People

Beijing maintains that its military -- the world's largest -- is aimed at securing peace rather than engaging in disputes with its neighbours over territory in the East and South China Seas.

China has been involved in occasionally tense confrontations with Japan and the Philippines over maritime disputes, generating fears that the rows could result in armed clashes.

Tokyo's Chief Cabinet Secretary Yoshihide Suga told reporters: "Countries including Japan are keenly interested in increased transparency of China's defence policies, including defence spending, as well as its military capability."

- Lessons from history -

Beijing frequently defends the expansion of its military by pointing to the "century of humiliation" the country endured during its partial occupation by foreign powers, including Japan, in the 19th and 20th centuries.

NPC spokeswoman Fu Ying told reporters Wednesday, ahead of the budget's official release, that China will never forget its lesson from history: "Those who fall behind will get bullied."

But questions have been raised over the effectiveness of China's fighting forces, which have been among the targets of a wide-ranging corruption crackdown under President Xi Jinping, who is also general secretary of the ruling party and chairman of its Central Military Commission (CMC).

Around a dozen generals have been ensnared, and Li said Beijing would "uphold the fundamental principle of the Party's absolute leadership over the armed forces".

Former CMC vice-chairman Xu Caihou confessed to bribery last year and was dismissed from the military with his rank revoked last year, military prosecutors said.

Top officer Gu Junshan was formally charged with corruption after he was exposed as owning dozens of homes, state media reported. Officials seized "a gold boat, a gold wash basin and a gold statue of Mao Zedong" along with "crates of expensive liquor" from one of Gu's residences, reports said at the time.

China has resolutely asserted its territorial claims since Xi came to power two years ago, but he has previously spoken of Beijing being incapable of "hegemony or militarism", saying "it is not in the genes of the Chinese".

The finance ministry report containing the budget figures said China would "strive for the goal of building powerful armed forces" to "safeguard China's sovereignty, security, and territorial integrity, and so that they ensure its peaceful development".

Bitzinger said the term "peaceful development" had become more widely used by Beijing, as it was less "aggressive" than the previous term often used by Chinese officials, "peaceful rise".

"But this is a military, and militaries do not really have anything to do with peace, they have everything to do with war," he added.