China Thursday launched a series of blistering attacks on key rival Japan after a defence paper approved by Tokyo criticised Beijing's military build-up and growing territorial assertiveness.

China's foreign ministry branded the paper "irresponsible," insisting Beijing's drive to modernise its forces was entirely defensive, and expressed its "strong dissatisfaction".

State news agency Xinhua went further, accusing Japan of "China bashing" and warning the document could jeopardise relations between the neighbours, while the defence ministry also issued a statement condemning the paper.

Japan's annual defence report, released this week, voiced concern over China's growing assertiveness in the South China Sea and Pacific Ocean, and what it called the "opaqueness" of Beijing's military budget.

"The Japanese 2011 defence white paper made irresponsible comments on China's national defence construction. China expresses its strong dissatisfaction," foreign ministry spokesman Ma Zhaoxu said.

"China's development is offering significant opportunities to all countries -- including Japan -- and China has not been, and never will be a threat to any other country."

China broke off all high-level contact with Tokyo last September after Japan detained a Chinese fishing boat captain whose vessel collided with Japanese coast guard patrol ships in waters claimed by both sides.

The row between Asia's two biggest economies was their worst in years and undermined painstaking recent efforts to improve relations marked by decades of mistrust stemming from Japan's 1930s invasion of China.

The Chinese skipper was released after more than two weeks and the two countries, which have deep trade ties, have been trying to mend fences.

The Japanese report, approved by Prime Minister Naoto Kan's cabinet, used a word that can be translated as "overbearing" or "assertive" for China's stance in the disputes with its neighbours, including Japan.

"We used the expression, thinking the entire international community probably perceives it that way," said Japan's Defence Minister Toshimi Kitazawa.

"This is one way of expressing our hope that China will address these issues through friendly relations."

The paper also said China's defence spending was not transparent, saying that the budget publicly announced by China "is widely seen as only part of what Beijing actually spends for military purposes."

"Opaqueness in its defence policies and military movements are concerns for the region, including Japan, and for the international community, and we need to carefully analyse them," it said.

Xinhua called claims "groundless" and said the report "dutifully carries out its China-bashing tradition, nitpicking at China's defence expenditure growth and military modernisation in the manner of a back seat driver".

Earlier this year, China announced military spending would rise 12.7 percent to 601.1 billion yuan ($91.7 billion) in 2011 after funding slowed last year.

Beijing has repeatedly sought to alleviate fears over its pursuit of sophisticated missiles, satellites, cyber-weapons and fighter jets, stressing that its policy is "defensive in nature."

It has invested heavily in developing its first stealth fighter jet, revealed in January, as well as an aircraft carrier and anti-ballistic missile capable of piercing the defences of even the most sturdy US naval ships.

However, China has become increasingly assertive in its claims over the East China Sea and South China Sea, most of which it views as its maritime territory, but where several other Asian nations have competing claims.