Southeast Asian nations have agreed to hold their first-ever joint military drills in the South China Sea, Indonesian officials said Thursday, as tensions grow over China's increasing assertiveness in the region.

"We will hold joint military drills in the North Natuna Sea," Indonesian military chief Yudo Margono said after a meeting of Southeast Asian defence chiefs in Bali, state news agency Antara reported.

They will take place in September involving all 10 members of the Association of Southeast Asian Nations (ASEAN) bloc and observer member Timor-Leste, he said.

That would include junta-ruled Myanmar, where the military has overthrown a civilian leader and overseen a bloody crackdown on dissent that has resulted in wide-ranging US and EU sanctions.

Margono said the exercises will focus on maritime security and rescue, and will not involve combat operations.

"It is about ASEAN centrality," he said.

The bloc's members have held naval drills with the United States before but never military exercises as a bloc on its own.

The announcement comes after Washington called on Beijing to stop "provocative" behaviour in the disputed waterway after a near-collision with a Philippine vessel and a Chinese fighter pilot's dangerous manoeuvre near an American surveillance aircraft.

Chinese vessels have also occasionally intruded into the Indonesian-claimed waters of North Natuna where the drills will take place, prompting protests in Jakarta.

China says most of the South China Sea is its own despite competing claims from other Southeast Asian nations including Indonesia, Vietnam, the Philippines and Malaysia.

Beijing's ships have patrolled the area and when confronted have invoked China's so-called nine-dash line -- an area it claims but is contested by its neighbours -- to justify its alleged historic rights to the waters.

At a summit last month, ASEAN leaders discussed "serious incidents" in the South China Sea and ongoing negotiations for a code of conduct aimed at reducing the risk of conflict there.

ASEAN has long been decried by critics as a toothless talking shop, and its charter principles of consensus and non-interference have hamstrung its ability to take action.

The bloc will hold its next leaders' summit in Indonesian capital Jakarta in September.