Vietnam on Friday slammed "groundless" territorial claims in Asian waters and called for self-restraint among nations involved in disputes.

Speaking at a security conference in Singapore, Vietnamese Prime Minister Nguyen Tan Dung said building "strategic trust" was the key to continued peace, cooperation and prosperity in the Asia-Pacific region.

However, he warned that sovereignty and territorial disputes in the South China Sea and the East China Sea were "evolving with great complexity", threatening maritime security and freedom of navigation in those areas.

"Somewhere in the region, there have emerged preferences for unilateral might, groundless claims and actions that run counter to international law and stem from imposition of power politics," Dung said in a keynote speech to the annual conference known as the Shangri-La Dialogue.

Dung did not specify any one country, but Vietnam and the Philippines are the most vocal states in the Association of Southeast Asian Nations (ASEAN) in opposing Beijing's claims in the South China Sea.

China says it has sovereign rights to nearly all of the sea, including waters and territories much closer to other countries and thousands of miles away from the Chinese coast.

ASEAN members the Philippines, Vietnam, Malaysia and Brunei, as well as Taiwan, also claim parts of the sea, which is believed to sit atop huge deposits of oil and gas and is home to some of the world's busiest shipping lanes and richest fishing grounds.

Competing claims have for decades made the area one of Asia's potential flashpoints for military conflict. China and Vietnam fought battles in 1974 and 1988 for control of islands that left dozens of soldiers dead.

Tensions have risen again in recent years as China used increasingly aggressive diplomatic and military tactics to assert its claims.

Among the moves that have caused alarm were China's occupation of a shoal close to the Philippines' main island last year, and the deployment in March of Chinese naval ships to within 80 kilometres (50 miles) of Malaysia's coast.

Manila this month also protested what it said was the "provocative and illegal presence" of a Chinese warship near Second Thomas Shoal, but Beijing dismissed the complaint, insisting that the area was part of its territory.

In his speech in Singapore, Dung said Vietnam adhered to the principle of peacefully settling disputes and urged others to do the same.

"All parties concerned need to exercise self-restraint and must not resort to force or (the) threat to use force," he said.

He called on ASEAN and China to work together on a legally binding code of conduct to prevent conflict in the South China Sea.

The conference gets into full swing on Saturday, with US Defense Secretary Chuck Hagel expected to press China on cyber attacks and reaffirm Washington's strategic shift to the Asia-Pacific region.

Chinese Lieutenant General Qi Jianguo, deputy chief of general staff of the People's Liberation Army, will address the forum on Sunday.