After meeting his Vietnamese counterpart in Hanoi, Scott Morrison said the leaders remained committed to independence and sovereignty in the region.

While Australia has hinted at the issue, it has never explicitly condemned China's actions and military build-up in the South China Sea, where Vietnamese and Chinese vessels are locked in a tense standoff in Vietnam-controlled waters.

Mr Morrison was asked why he once again called out the behaviour — but not the perpetrator.

"It isn't about picking sides," he said.

"It's about ensuring each and every nation in this region can have confidence in its independence and sovereignty."

Vietnamese Prime Minister Nguyen Xuan Phuc discussed the rising tensions in the South China Sea with Mr Morrison, during his first visit to Hanoi since the countries formalised their "strategic partnership" earlier this year.

"We are deeply concerned about the recent complicated developments in the East Sea and agree to cooperate in maintaining peace, stability, security, safety and freedom of navigation and overflight," said Mr Phuc, using the Vietnamese name for South China Sea, while standing alongside Mr Morrison.

The comments were Mr Phuc's first on the standoff.

A Chinese vessel, the Haiyang Dizhi 8, continued to survey Vietnam's exclusive economic zone on Friday under escort from at least seven Chinese vessels, according to data from Marine Traffic, a website that tracks vessel movements.

At least two Vietnamese navy ships, including the Russian-built Quang Trung frigate, have been closely shadowing the Chinese vessels, according to the data.

Trade features as leaders meet

Bilateral trade rose 19.4 per cent in 2018 to $7.72 billion, according to Vietnamese Government customs data.

Australia is the largest foreign coal supplier to Vietnam, which is increasingly reliant on the fossil fuel for power generation to meet its fast-growing economy.

Coal shipments from Australia to Vietnam more than tripled in the January-to-July period from a year earlier, to 8.51 million tonnes, according to customs data.

Mr Morrison said he hoped his visit would help strengthen trading ties between the two countries.

"Prime Minister Nguyen Xuan Phuc and I are friends, Australia and Vietnam are friends," he said.

"Today, to use an Australian phrase, we have gone from friends to mates."

Australian Brodcasting Corporation with Reuters - August 23, 2019