China on Saturday vowed "clear and firm reactions" to defend its interests in the South China Sea but rejected suggestions of aggression, as Beijing faces international pressure over maritime disputes with its neighbours.

A series of incidents between Beijing and rival claimants to the waters has sent regional tensions soaring and spurred Washington to call for an end to all "provocative" acts.

"The position of China to safeguard its own sovereignty, maritime rights and interests is firm and unshakeable," Chinese Foreign Minister Wang Yi told reporters following a meeting with the Association of Southeast Asian Nations (ASEAN) in the Myanmar capital Naypyidaw.

Wang said the situation in the contested waters was currently "stable," adding that Beijing always acted with "self restraint".

"However, for those groundless provocative activities, the Chinese side is bound to make clear and firm reactions," he said.

US Secretary of State John Kerry, who arrived in the early hours of Saturday to attend a series of meetings with regional and international powers, is expected to underline Washington's message for a freeze on any activities that could worsen regional maritime relations.

Animosity over the South China Sea, a crucial maritime route that is also believed to hold huge oil and gas deposits, is dominating ASEAN talks, which began Friday and are broadening to include key world powers ahead of security discussions on Sunday.

Beijing claims sovereignty over almost the entire sea including waters, islands, reefs, shoals and rocky outcrops nearer to other countries.

ASEAN states Brunei, Malaysia, the Philippines and Vietnam also claim parts of the sea, while Taiwan is a sixth claimant.

Ties between China and Vietnam sank to their lowest point in decades in May after Beijing moved a deep-sea oil rig into disputed waters near the Paracel Islands, triggering deadly anti-China riots in Vietnam.

Beijing has since removed the rig, in a move that analysts say was aimed at deflecting accusations of aggression.

- US charm offensive -

Kerry kicked off his Southeast Asian diplomatic charm offensive with a meeting with his Vietnamese counterpart Pham Binh Minh.

The top US diplomat, who fought in the Vietnam War, hailed "progress" in relations, adding that issues such as communist Vietnam's rights record would continue to be discussed as part of efforts "to really bring this relationship to its full blossom".

The US is looking to reinvigorate alliances in the Asia-Pacific as part of President Barack Obama's foreign policy pivot to the region.

Washington has said discussions of the South China Sea at the ASEAN Regional Forum on Sunday are expected to be robust, but a state department official said the US was not looking for a "showdown" with China.

The forum is an annual security dialogue among foreign ministers of the 10-member ASEAN and key partners, including the US, Australia, China, India, Japan, South Korea, Russia and the European Union.

A draft statement from ASEAN foreign ministers, who met Friday, said the 10-member bloc had "serious concern" over recent developments in the disputed sea.

It also called for an end to "destabilising actions" in wording that is likely to have proved contentious for China's supporters in ASEAN -- no final statement had been released by Saturday afternoon.

The Philippines has been at the forefront of protest against China and has challenged Beijing's claims before a UN tribunal.

In March, China tried to block a resupply mission by Manila to a shoal in the Spratlys, after also seizing another South China Sea shoal from the Philippines in 2012.

"I asked everyone to see that the situation (in general) was getting to a point where it would no doubt begin to affect the peace, security and stability of the region," said Philippine Foreign Secretary Albert del Rosario late Friday.

Manila wants a speedy conclusion of talks for a legally binding code of conduct, and the establishment of a dispute settlement mechanism anchored in international law.

China's Wang said Beijing was ready to listen to "well-intentioned proposals" and urged Manila to drop the case it filed with the United Nations.

Beijing favours bilateral dispute negotiations, an approach rejected by other claimants.