Japan's government will press ahead with divisive plans to loosen restrictions on its military, a top government spokesman said Monday, despite widespread public anger and a protester's horrific suicide bid.

Hundreds of people in the busy Tokyo district of Shinjuku watched on Sunday afternoon as a middle-aged man in a suit set himself ablaze above a footbridge, after making a speech opposing moves to let Japan's well-equipped military fight on behalf of allies.

The dramatic suicide attempt was widely discussed on social media in both English and Japanese, with numerous videos and photographs posted by onlookers.

Many Internet users made the connection between the self-immolation and a groundswell of opposition to Prime Minister Shinzo Abe's push to relax constitutional rules preventing Japan's armed forces from going into battle.

Abe says growing regional tensions -- including China's increasingly assertive stance in various territorial disputes -- and the erratic actions of North Korea mean Japan must be better prepared to defend itself.

The conservative premier's plans to increase Japan's military options are supported by the United States, Tokyo's chief ally, but are highly controversial at home, where voters are deeply wedded to the pacifism Japan adopted after World War II.

The government's chief spokesman Yoshihide Suga on Monday refused to comment on the protester's suicide attempt, which he said was a police matter, but confirmed that the cabinet would push ahead Tuesday with plans to change the interpretation of part of the pacifist constitution.

Under the current reading, Japan's large and well-trained military is barred from taking any action, except in very narrowly defined circumstances in which the country is under attack.

"We are in the final stage of the coordination between the ruling parties," Suga told reporters. "Once the consensus is made between the ruling parties, we will have it approved by the cabinet tomorrow."

- Strong public opposition -

The latest polls suggest at least half the population is against a more aggressive military stance.

The liberal Mainichi newspaper said at the weekend that 58 percent of voters are opposed, while the Nikkei business daily, in its poll published Monday, said 50 percent of respondents were against the change.

China also warns against moves to bolster Japan's military robustness, saying Tokyo is not sufficiently penitent over its actions in World War II.

It sent two ships into waters around disputed islands on Monday, a regular tactic in the long-running animosity.

But Suga defended the plan, saying: "The government should protect people's lives and property as well as the country's safety ...and if there is a defect in the current legal framework, we will address it."

Tokyo police said Monday that nothing was known of the protester's condition more than 24 hours after he was rushed to hospital with severe burns.

The suicide bid received scant coverage in the mainstream media -- which is sometimes criticised as servile -- with none of the national newspapers using a picture in their short reports.

Broadcaster NHK, whose chairman caused outrage earlier this year by suggesting that the state-funded body should not contradict the prime minister, did not cover the self-immolation on the day.

At least two private broadcasters did, however, using footage that had been posted on YouTube.

Popular protest in Japan has tended over recent decades to be muted, and protest suicides are very rare, with only a handful taking place in living memory.

In 1970, right-wing novelist Yukio Mishima disemboweled himself after a failed attempted coup, in protest against what he saw as an overly meek state.

In 1967, a 73-year-old man set himself alight in front of the prime minister's official residence over the then-premier's support for US bombing of North Vietnam.

Abe had wanted to change the constitution to lower the bar for military action, but found himself unable to muster the required super-majority in both houses and leery of the public verdict in the necessary referendum.

Instead, he has gone the route of changing how the constitution is interpreted, a tactic supporters say is necessary to avoid the paralysis that often besets Japanese politics, but which critics say undermines democracy.

Hideki Konishi, professor of politics at Kansai University, said it serves neither side.

"Changing the rules by a cabinet approval only is not good for either supporters of collective self-defence or opponents," he said.

"This means that rules can change whenever there is a change of government."