Japan on Tuesday slammed Beijing's bid to reclaim land in the South China Sea as a "coercive attempt" to force sweeping maritime claims, in a defence paper that comes as Tokyo is expanding the role of its own military.

Tokyo said China was acting "unilaterally and without compromise", as it also highlighted concern about North Korea's nuclear programme and Russian moves in violence-wracked Ukraine.

The white paper accused Beijing of "raising concerns among the international community" as it ramped up criticism from last year's report, an annual summary of Japan's official view on defence matters.

"China, particularly over maritime issues, continues to act in an assertive manner, including coercive attempts at changing the status quo, and is poised to fulfil its unilateral demands without compromise," said the report entitled "Defense of Japan 2015".

China is locked in disputes with several countries over its claims to almost the entire South China Sea and is currently pursuing a rapid programme of artificial island construction in the region.

It is also embroiled in a separate row with Japan over the Tokyo-controlled Senkaku islands -- which it calls the Diaoyus -- in the East China Sea, as Chinese ships and aircraft regularly test Japanese forces in the area.

While the Sino-Japanese spat has cooled considerably over the last 12 months or so, observers had warned that it could spiral into a limited armed conflict.

Separately, Japan has complained that China may have started offshore drilling for gas in the disputed waters.

"Japan has repeatedly lodged protests against China's unilateral development and demanded the termination of such works," the report said.

The document repeated Tokyo's concerns over China's growing assertiveness and widening naval reach in the Pacific and over what it calls the "opaqueness" of Beijing's sky-rocketing military budget.

But it also noted that China has worked to set up an emergency hotline with Tokyo to prevent unintended conflicts at sea.

- 'Harsher security environment' -

Last week, China criticised Tokyo after the lower house of parliament passed bills that could see Japanese troops fight abroad for the first time since World War II, in provisions that allow for so-called "collective defence" -- coming to the aid of allies under attack.

A fraught mutual history makes Beijing particularly sensitive to any suggestion that Japan may abandon its pacifism.

Millions of Chinese died in the years after Japanese forces launched a full-scale invasion of the country in 1937.

But Tokyo's move to give greater leeway to its well-equipped and well-trained military is far from popular at home, and polls show approval ratings for Prime Minister Shinzo Abe -- the driving force behind the changes -- are plunging.

A new weekend poll showed just 35 percent of voters positively rated Abe, his lowest level since coming to power in 2012.

"We hope to explain to the public that the bills are necessary amid a harsher security environment around Japan," the government's top spokesman Yoshihide Suga told reporters Tuesday, asked about unpopularity of the bills and the government.

Referring to the Ukraine crisis, the report said Russia "has engaged in so-called 'hybrid warfare' that is difficult to identify definitively as an armed attack by a country, and has attempted to change the status quo by force or coercion".

"The Russian attempt is considered to be a global security issue possibly affecting the whole international community, including Asia," it said.

On North Korea, the report warned of a "greater risk" of Pyongyang deploying ballistic missiles mounted with nuclear warheads "that include Japan in their range".