World leaders from more than a dozen countries including the US, Russia and China are attending the regional economic summit. A dispute over South China Sea territory is a sticking point between Beijing and Washington.
Ten southeast Asian heads of state and nine world leaders, including US President Barack Obama, are meeting on Friday in Malaysia to discuss trade and economic issues.
Malaysia tightened security in the capital Kuala Lumpur following the recent deadly attacks on civilians in France, Egypt and Lebanon - saying it had received unconfirmed reports of a plot.
"There have been reports of imminent terrorist threats in Malaysia," Malaysia's police chief Khalid Abu Bakar said in a statement on Thursday night. "At this point, I would like to underline that they have yet to be confirmed."
US President Barack Obama is joining leaders of the 10-member Association of South East Asian Nations (ASEAN) for the weekend summit in Kuala Lumpur.
Leaders from seven other countries with close partnerships with the grouping - Australia, China, India, Japan, New Zealand, Russia and South Korea - will also attend the meetings starting on Saturday.
At least 2,000 Malaysian troops are being stationed at strategic points in Kuala Lumpur and another 2,500 are on standby, the country's armed forces chief Zulkifeli Mohd Zin said ahead of world leaders' arrival.
Through land reclamation, China has created artificial islands from reefs to bolster its territorial claims to strategic shipping lanes in the South China Sea.
South China Sea dispute over 'islands'
The ASEAN group has not taken a collective stand about China's increasingly assertive stance in the South China Sea in which it has constructed artificial islands to lay claim to territorial waters that are currently used as a major international seaway. ASEAN's secretary general said it was no surprise member countries are looking for constructive ways to resolve the dispute.
"They have the right to take any path or any process, as long as its a peaceful one conducive to a solution of the dispute," ASEAN Secretary General Le Luong Minh told Reuters news agency.
But Beijing's claim to almost the entire South China Sea is shown on Chinese maps with a nine-dash line that stretches deep into the heart of Southeast Asia. This clashes with current claims by Vietnam, the Philippines, Malaysia, Taiwan and Brunei.
The US recently flew B-52 bombers near the islands, signaling Washington's determination to challenge Beijing over the disputed sea.
China has said it does not want the dispute to be the focus of the meetings in Kuala Lumpur and a draft of the chairman's statement to be issued at the end makes no mention of the recent tensions.
ASEAN agreements are based on consensus, with each member country's position taken into consideration before any collective decision is made. But this non-confrontational principle has been criticized as a weakness of the organization as recent meetings have broken up after failing to reach a consensus.
jar/msh (Reuters, AP, dpa)