Southeast Asian leaders gathered in Bangkok on Saturday determined to drive forward the world's largest commercial pact, with the trade war between the US and China clouding the outlook for their export-led economies.

Disputes in the flashpoint South China Sea and Myanmar's persecution of Rohingya Muslims are expected to be tussled over by leaders on Sunday, the final day of the Association of Southeast Asian Nations (ASEAN) summit.

But trade has taken centre stage with ASEAN leaders keen to hasten the signing of a China-drafted commercial deal covering around half the world's population.

The Regional Comprehensive Economic Partnership (RCEP) includes all 10 ASEAN economies, plus India, Japan, South Korea, Australia and New Zealand.

It is seen as a mechanism for China to draft the rules of Asia-Pacific trade, following a US retreat from the region.

While tit-for-tat tariffs between the world's biggest two economies have seen some manufacturers flee China to safer ASEAN hubs, economists say the big picture for global growth is bleak and member countries are keen to boost trade with the RCEP.

A draft of the chairman's statement seen by AFP said the bloc was committed to finishing RCEP "negotiations within this year" and would "exert relentless efforts to reach this target."

"The faster it (RCEP) gets implemented the better," Martin M. Andanar, Philippines Communications Secretary, told reporters earlier.

Progress on the deal has stuttered in recent months with India digging in over fears cheap Chinese goods could flood its massive consumer market.

- Rohingya talks -

ASEAN is frequently criticised as a soft forum where diplomatic niceties often outweigh concrete action on pressing problems.

Foreign ministers discussed the repatriation of more than 740,000 Rohingya refugees that have fled Myanmar into Bangladesh.

Malaysia, which speaks up most strongly for the Rohingya, said the perpetrators of violence against the Muslim minority must "be brought to justice".

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Repatriation "must include the citizenship of the Rohingya," Malaysian Foreign Minister Saifuddin Bin Abdullah said according to a tweet by his ministry.

Myanmar's de facto leader Aung San Suu Kyi is in Bangkok for the meeting.

ASEAN has come under fire for suggesting the refugees should go back to Myanmar within two years, according to a leaked report seen by AFP -- though virtually none have volunteered to return so far, citing safety concerns.

The bloc also agreed on Saturday to "take concrete actions in combating" marine debris -- including plastic -- across the region in the "Bangkok Declaration", though activists have said it doesn't go far enough in curbing single-plastic use.

Regional leaders are set to continue to tackle thorny South China Sea issues on Sunday, with a draft Code of Conduct agreement up for review. Observers however doubt any major progress will be made.

Discussions so far have been overshadowed by a recent dust-up in the sea between a Chinese ship that rammed a Filipino fishing boat and caused it to sink.

Beijing claims most of the resource-rich waterway.

Manila said a joint investigation into the incident has been launched, adding that the run-in would not derail Code of Conduct talks.

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