China accused Japan of threatening regional peace Saturday after Tokyo passed laws clearing Japanese troops to fight abroad for the first time since World War II, saying that its rival should learn "profound lessons from history".

Japan's ruling coalition, led by nationalist Prime Minister Shinzo Abe, pushed the laws through in the early hours of Saturday morning after days of tortuous debate that at times descended into physical scuffles in parliament.

For the first time in 70 years, the new laws will give the government the power to send the military into overseas conflicts to defend allies, even if Japan itself is not under attack.

China's defence ministry said Saturday the reforms had "aroused grave concern among its own citizens, Asian neighbouring countries and the international society," state media reported.

A Xinhua editorial added that Japan's new security bills "not only broke Japan's promise to the world after World War II, but also betrayed its own people".

Japan's nationalist premier has argued the laws are necessary to protect against threats from what it views as an increasingly belligerent China and unstable North Korea, but opponents fear the vague wording could see Japan dragged into far-flung foreign wars.

South Korea called on Japan to remember the need for transparency in implementing its new defence policy "while maintaining the spirit of the pacifist constitution," its foreign ministry said in a statement cited by the Yonhap news agency.

North Korea's official KCNA news agency later released a strongly-worded statement from the foreign ministry accusing Japan of being "obsessed with an anachronistic ambition for reinvasion".

"Japan's militarist moves are posing a grave threat to peace and stability in Asia and the rest of the world," the statement added.

It warned the North "will further increase the war deterrence to cope with the dangerous moves for aggression against it".

- 'This is not an end' -

Abe has faced bitter opposition at home over the changes, which have seen his popularity slump, and opposition lawmakers have vowed to do everything in their power to fight them.

"This is not an end," said Renho, a senior lawmaker from the main opposition Democratic Party of Japan, who goes by one name.

"Let's make it the beginning of the beginning," she said on Twitter.

Mizuho Fukushima, a senior lawmaker from the opposition Social Democratic Party, told a crowd of more than ten thousand who gathered outside parliament during the debate: "Abe's cabinet criminals... Let's get them out of here."

Speaking after the vote, Abe said the changes were "necessary in order to protect people's lives and peaceful way of life".

"This is designed to prevent wars," he told journalists.

Abe had been unable to muster support to amend the pacifist constitution and instead opted to "re-interpret" the meaning of self-defence in order to push through the new laws, but the move has sparked a groundswell of opposition not seen for decades in Japan.

A hardcore group of some 300 protesters gathered outside parliament on Saturday, calling for the legislation to be abolished and vowing never to stop their fight against Abe.

"Our battle will never end. This is just the beginning," Keisuke Yamamoto, an organiser from one of the citizen groups that have been leading weeks of rallies, told AFP.

"We will resort to every possible measure, including bringing the case to the courts... We can't let this movement fizzle out now."

Behind him, demonstrators carried banners or billboards, which read: "We should not get children killed," and "Don't let them wage a war".

- 'Black stain' -

Legal scholars have argued the legislation violates Japan's pacifist constitution, imposed by the US after World War II, and several groups on Saturday said they were preparing to challenge the new laws.

Susumu Murakoshi, chairman of the 36,000-strong national bar association, on Saturday criticised the government for going against the will of the people and pledged to see the changes abolished.

The laws have "left a black stain on the history of Japan as a constitutional democracy," he said in a statement.

National broadcaster NHK reported that respected constitutional scholar Setsu Kobayashi, from Keio University, is already planning to muster 1,000 lawyers to file a challenge to the legislation in the Tokyo district court.

Legal action aside, the laws will likely take months to come into effect and the supreme court could urge lawmakers to amend them.

Even under the new legislation, Japan's military will still be more restricted than other countries: parliament will have to approve any deployments, based on strict criteria, and force must be kept to a minimum.

Tokyo has said the changes would allow troops to help their American counterparts, but officials have remained tight-lipped on who else it would cover.

It could include the Philippines, or Australia, both of which Japan has forged closer military ties with in recent years, and the new laws were welcomed by the Australian Foreign Minister Julie Bishop.

"These reforms will allow Japan to make a greater contribution to international peace and stability," she said in a statement Saturday.