As South Korea begins another series of naval exercises despite warnings from the North, the Chinese president Hu Jintao has told Barack Obama that tensions in the region could spiral out of control.
The US and Japan are also holding large scale military exercises.
China faces calls from Washington to do more to curb its ally North Korea.
The US is hosting talks with Japan and South Korea on how to deal with Pyongyang. They are expected to condemn formally the recent attack on Yeonpyeong island, hit by a barrage of North Korean shells nearly two weeks ago.
The latest drills are taking place to the west, east and south of the peninsula, including near the disputed Northern Limit line which is not recognised by the North.
The 29 locations include one island near the Yellow Sea border – but the exercises are steering clear of Yeonpyeong.
South Korea has held funerals for two civilians killed in the bombardment from the North. Four people were killed in all, including two marines, and dozens of houses were destroyed.
Seoul has since been threatening a tougher response against the North in the event of another expected attack.
President Obama has urged Beijing to send a clear message to North Korea that its provocations are unacceptable.