JOIN USA photographer allowed in for the start of the meeting said that Wen and Obama were sitting next to each other, with U.S. officials, including Secretary of State Hillary Clinton and Obama's national security adviser Tom Donilon also, attending.
Wen and Obama were engaged in small-talk as the meeting began. Print reporters were not allowed in to the start of the talks.
A Chinese diplomat told Reuters it would be a "small scale" meeting, providing no other details. A U.S. official said it would likely be brief.
The two countries have disagreed over how to handle disputes over sovereignty of the South China Sea. The United States is pressing for open dialogue at the summit, while China wants to deal directly with other claimants; Vietnam, the Philippines, Taiwan, Malaysia and Brunei.
Obama is the first U.S. president to attend the East Asia Summit, a regional bloc of Southeast Asian countries plus eight dialogue partners, including the United States and Russia from this year.
The U.S. president is wrapping up a nine-day Asia-Pacific tour where he has sought to re-assert the United States' role as a Pacific power with an increased U.S. military presence in Australia and more trade and strategic ties with a range of Asian nations, raising stress levels in Beijing.