Beijing sought to soothe tensions over its South China Sea claims Saturday, saying it will avoid the use of force in the region as the US ponders sending warships close to territory claimed by the Asian giant.

Speaking at the Xiangshan regional defence forum in Beijing, Fan Changlong, vice-chair of China's Central Military Commission, pledged that the country would "never recklessly resort to the use of force, even on issues bearing on sovereignty".

"We have done our utmost to avoid unexpected conflicts," he added.

The US says that China's transformation of South China Sea reefs into artificial islands capable of hosting military facilities presents a threat to freedom of navigation, and defence officials have hinted they may soon use naval forces to test Chinese claims.

But Fan said that the projects were mainly intended for civilian use and "will not affect freedom of navigation in the South China Sea".

"Instead, they will enable us to provide better public services to aid navigation and production in the South China Sea."

The argument is one Beijing has made many times before, but satellite images of the islands published by the US think-tank Center for Strategic and International Studies have shown as many as three runways on the islands that could accommodate fighter jets, raising concerns about China's true intentions.

Speaking in Washington this week, Pentagon chief Ashton Carter said the US would continue to sail wherever international law allowed.

While no American officials spoke at the event, the country's retired Chief of Naval Operations Gary Roughead used his time on a morning panel to take China to task for its behaviour.

"The rapid expansion of land features in the vital sea lanes of the South China Sea heightens suspicion and presents the potential for miscalculation," he said.

The construction, he added, "raises legitimate questions regarding militarisation".

"I do not see an influx of tourists clamouring to visit these remote islands," he said.

- 'Unintentional incidents' -

The dispute between the two goliaths, the region's largest military and economic powers, has unnerved members of the Association of Southeast Asian Nations (ASEAN), who are caught in the middle of the standoff.

Speaking to reporters after Fan's remarks, Malaysian Defence Minister Hishammuddin Hussein said that the US has briefed him on its plans, but "counterreaction by major powers in the region sometimes is beyond the control of small nations".

"My concern is unintended, accidental, unintentional incidents in the high sea, especially between two major powers," he said.

Hussein was one of several cabinet-level participants attending the event from the 10-member ASEAN bloc, which includes Brunei, Malaysia, the Philippines and Vietnam, all of which have rival South China Sea claims.

Taiwan, a non-ASEAN member, is also a claimant.

Fan's "statement was reassuring to us all", Hussein said in remarks during a morning session, but cautioned that the best way to address concerns was the establishment of a code of conduct for claimants in the region.

ASEAN has for years called on China to negotiate such an agreement, which would put into place a binding set of rules aimed at preventing actions that lead to conflict.

The Xiangshan forum is a security dialogue China has recently pushed as part of a broader effort to increase its global influence.

Vietnam's Defence Minister will address maritime security issues during a panel Sunday. An official from the Philippines will also appear during the conference.

Hanoi has repeatedly accused China of ramming its fishing boats as they ply local waters, while Manila has infuriated Beijing by taking their dispute to a United Nations tribunal.