China has evacuated more than 3,000 of its nationals from Vietnam following a wave of deadly anti-Beijing unrest, state media said Sunday, as Vietnamese civil society groups called for renewed demonstrations in several cities.

The Xinhua news agency said the evacuees included 16 nationals who were "critically injured" in the worst anti-China violence in Vietnam in decades triggered by Beijing's deployment of an oil rig in contested South China Sea waters.

They were pulled out on a chartered medical flight and China was dispatching five ships to Vietnam to pluck more nationals to safety, after an alliance of 20 vocal Vietnamese NGOs called for fresh protests Sunday in the capital Hanoi, the southern economic hub of Ho Chi Minh City, and other areas against China's "aggressive actions" in the South China Sea.

But Vietnamese authorities, which have occasionally allowed protests to vent anger at the country's giant neighbour, warned they would "resolutely" prevent any further outbursts.

China's positioning of an oil rig in waters also claimed by Vietnam has ignited long-simmering enmity between the two communist neighbours, which have fought territorial skirmishes in past decades.

Worker demonstrations spread to 22 of Vietnam's 63 provinces in the last week, according to the Vietnamese government, with enraged mobs torching foreign-owned factories. The violence left at least two Chinese workers dead and more than 100 injured.

More than 3,000 Chinese nationals had been evacuated from Vietnam as of Saturday afternoon, Xinhua reported early Sunday.

"They returned to China with the assistance of (the) Chinese Embassy to Vietnam," it said, citing China's foreign ministry.

Beijing has also advised its nationals against travelling to Vietnam.

"Recently, there was an explosion of violence in South Vietnam targeting foreign companies, provoking injuries and death of Chinese citizens and damaging companies' properties," China's foreign ministry said on its website Saturday.

"The foreign ministry advises Chinese nationals temporarily not to travel to Vietnam. (It also advises) Chinese citizens and structures in Vietnam to increase their risk-awareness, to strengthen their security prevention measures, and to avoid leaving (their premises)."

Xinhua also reported that security chief Guo Shengkun had spoken to his Vietnamese counterpart and urged the authorities there to quell the violence, adding that Commerce Minister Gao Hucheng had also called on officials to "bring relevant issues under control".

Call for fresh protests

The alliance of local Vietnamese NGOs has renewed calls for fresh protests in the country, however it urged participants to remain peaceful following the chaos Tuesday and Wednesday.

"Those violent actions created a bad image for patriotic demonstrations and the people of Vietnam; therefore, they must be stopped," said a statement issued on social media late Friday.

The alliance comprises largely of anti-government organisations and is believed to have played a role in stirring the recent protests.

In a text message sent by the government to Vietnamese mobile phone users Saturday, Prime Minister Nguyen Tan Dung said authorities across the country had been ordered to "implement measures to resolutely prevent illegal demonstrations that could cause social and security disorder".

China's deployment of the giant rig is viewed in Hanoi as a provocative assertion of Beijing's hotly-disputed claims in the South China Sea, and has been criticised by Washington as exacerbating territorial tensions.

There have been repeated skirmishes near the controversial rig in recent days between Chinese and Vietnamese vessels, including collisions and the use of water cannon.

The violent attacks on Chinese personnel at foreign-invested factories in Vietnam have further aggravated the situation, with China accusing Hanoi of a role in the unrest.

The attacks on foreign enterprises – which included Chinese, Taiwanese and Korean businesses – appear to have spooked Vietnamese authorities, which depends heavily on foreign investment for economic growth.

But, while condemning China's maritime actions, the government has warned against further protests and pledged foreign investments would be protected.

Taiwanese President Ma Ying-jeou has ordered commercial jets to be on standby to evacuate Taiwanese nationals should violence escalate.

The island's China Airlines and EVA Airways have already provided extra chartered flights to Vietnam.

The oil-rig confrontation is the latest to spark alarm among China's Southeast Asian neighbours, which complain of increasing maritime intimidation by Beijing.

China claims nearly all of the South China Sea, which is believed to hold significant offshore energy reserves.