All Southeast Asian stock markets plunged in early trade on Monday, led by Indonesia as emerging markets remained under pressure on concerns over US Federal Reserve further tapering its stimulus this week and fears of a slowdown in China.

Indonesia's Jakarta Composite Index fell 2.9 per cent by mid-day, its lowest level since January 10, led by financial stocks.

"The Fed tapering policy and China's slowing growth caused investors to lose confidence in emerging markets, especially in Indonesia," said John Teja, director of Jakarta-based broker Ciptadana Securities.

"The big drop in Wall Street last Friday is also a reason for foreign investors to take profit in local market," he said, adding that foreign investors have been selling this morning on a net basis "reversing net buying this past two weeks".

Fed officials are seen cutting bond-buying by another US$10 billion at their regular two-day policy meeting beginning on Tuesday, while investors continued to fret about the impact of tightening credit conditions in China as Beijing seeks to curb growth in high-risk lending.

The SandP 500 posted its worst week since June 2012 in the week ended Friday as a selloff in emerging market assets fed through to wholesale pullbacks in equities.

Singapore share index touched its lowest since September 4 at one point and was down 1.3 per cent at 0615 GMT, led by over a three per cent fall in Jardine Matheson Holdings Ltd.

Malaysian shares were 0.9 per cent down, hovering around 3-1/2-month low, the Philippine index plummeted 1.7 per cent, while Vietnam index, the best performer in the region so far this year, was down 0.5 per cent on profit-booking in most large-cap stocks.

Thailand index fell two per cent to 1,288, led by energy and banks amid lingering political concerns a day after one of the leaders of anti-government protests in Bangkok was shot dead when violence erupted as demonstrators tried to block early voting for an election next week.

"Thailand market was pressured by Fed tapering and local political concerns," said Teerada Charnyingyong, a strategist with Phillip Securities.

"We weigh those effect 50:50. Meanwhile, the support level for this afternoon would be around 1,280 and likely that foreigners would stay on selling side."

Nomura in a research report said the current political tensions in Thailand will only slow, but not derail, the long-term development of the economy.

"Our new 12M SET index target is 1410 which factors in the current weak domestic economy and gradual improvement in the political situation in 2014."-- Reuters