Japan's PM says his country will play a greater role in regional security and support South-East Asian countries in territorial disputes with China.
Shinzo Abe made the comments at the Shangri-La Dialogue in Singapore.
The three-day summit involves the US and South-East Asian countries, and comes amid growing tensions between China, Vietnam and the Philippines.
Chinese officials said Mr Abe was using the "myth" of a China threat to strengthen Japan's security policy.
Japan-China ties have also been strained over disputed islands in the East China Sea.
'Seas and skies'
Mr Abe gave the keynote address at the Shangri-La Dialogue, also known as the Asia Security Summit, on Friday.
Japan, he said, would play "a more proactive role than it has until now in making peace in Asia and the world something more certain".
"Japan will offer its utmost support for the efforts of the countries of Asean [Association of Southeast Asian Nations] as they work to ensure the security of the seas and the skies."
Mr Abe added that he supported efforts by the Philippines and Vietnam to resolve territorial disputes with China.
Earlier this month, the Japanese prime minister called for a new interpretation of the country's constitution, which currently bans "the threat or use of force" to settle international disputes.
China, which had parts of its territory occupied by Japan during World War Two, has criticised the move.
On Friday, Chinese Vice-Foreign Minister Fu Ying, who is also at the summit, said Mr Abe was "trying to amend the security policy of Japan" in a move that was "worrying for the region".
Mr Abe had exacerbated regional tensions and the "myth" that China was "posing a threat to Japan", she added.
Analysts say that although some Asean members will be reluctant to antagonise China because of their economic and political ties, others are likely to welcome an increased role from Japan.
'Overplaying its hand'
China continues to unsettle its neighbours after declaring an air defence zone in the East China Sea and taking a more confrontational stance over disputed islands in the South China Sea, the BBC's Sharanjit Leyl in Singapore reports.
The forum is a chance for senior delegates from the region to meet face to face and attempt to resolve tensions, our correspondent adds.
Beijing claims a U-shaped swathe of the South China Sea that covers areas other South-East Asian nations say are their territory.
Analysis: Jonathan Marcus, BBC diplomatic correspondent
Mr Abe wants to step up support for countries locked in maritime disputes with Beijing. He condemned those who wished to"consolidate changesto the status quo" by dictating to others - another stab at China.
Mr Abe wants to change Japan's post-war consensus to allow the country to take a more active role in collective defence. And it wasn't just what Mr Abe said - it was where he said it.
There is no collective security organisation like Nato in Asia and thus the conference known as the Shangri-La Dialogue has become the main annual security "event" in the region.
This was the first time that a Japanese leader had given the keynote address there - a sure sign that Mr Abe wants Japan to take a more expansive role in the wider security debate.
On Tuesday, a Vietnamese fishing boat sank after it collided with a Chinese vessel near a controversial oil rig in the South China Sea, with both countries blaming the other for the incident.
Vietnam has protested against China moving its oil rig to waters also claimed by Hanoi, at a spot near the disputed Paracel Islands.
Meanwhile, the Philippines is in the process of taking China to a UN court over its territorial claims in the South China Sea.
US Defence Secretary Chuck Hagel said he would use the summit to raise issues "where we think China is overplaying its hand and presenting new challenges".