Taiwanese workers told of their fear as they hid from Vietnamese rioters who ravaged hundreds of foreign-owned factories in Vietnam during violent demonstrations against China this week, burning several to the ground.

The atmosphere remained tense in the southern provinces of Binh Duong and Dong Nai Friday, where demonstrators looted and torched the factories in protest at Beijing's deployment of an oil drilling rig in disputed South China Sea waters.

A local Taiwanese Chamber of Commerce official told AFP Friday that more than 500 factories were attacked in Binh Duong alone in the riots earlier in the week.

China has accused Hanoi of "connivance" with protesters.

Leading Taiwanese industrial group Formosa Plastics said Thursday that Vietnamese workers had "provoked and attacked" Chinese employees at their steel mill in central Ha Tinh province, where one Chinese worker was killed and at least 149 injured in the unrest.

A contractor for the company said colleagues had told him that they witnessed dozens of Chinese workers being dragged from a bus and beaten.

"I hid in the dorm during the riots and later sneaked out the steel plant and drove to Hanoi to take the plane home," said the contractor, Lee Chun-ye, who returned to Taipei on Thursday.

"I was really nervous whenever the traffic slowed down as I was worried that Vietnamese people would attack me in my car," he said.

A Taiwanese businessman who gave his family name as Chen said some 40 Taiwanese and Chinese managers at his furniture plant in Binh Doung province managed to escape with the help of a Vietnamese supplier, who hid them in his factory.

"I think the Vietnamese authorities tacitly consented to the rioters as long as they didn't kill anybody," Chen said from the airport in Taipei.

"We were very scared as police didn't turn up in time to help us."

The Taiwanese Chambers of Commerce in Vietnam said they were advising owners to temporarily close their factories next week to keep workers safe amid fears of fresh violence.

"There is no new violence for the moment but we are worried about the upcoming rallies on May 18," said Yang Yu-feng, honorary chairwoman of the body. "We have advised Taiwanese companies to ... close their factories on that day."

- 'This will hurt Vietnam's image' -

More than 500 Taiwanese factories in Binh Duong were damaged on Tuesday and Wednesday, Yang said. About ten were burnt down, while others had windows smashed and computers stolen.

"We were surprised by the extent of the riots," she said. "Some 300 baton-wielding motorcyclists rode into the industrial parks and attacked the factories one by one. Things got out of control quickly. People were in panic."

Taiwan's tech giant Foxconn, which assembles products for Apple and other top international brands, announced Friday that all workers in its Vietnamese facilities will be given three days off until May 19 "for their safety".

The factories are now assessing the losses while planning to seek compensation from the Vietnamese government. Taiwan has demanded Vietnam offer full compensation.

Yang estimated it would take at least a month for the damaged factories to resume operations, leaving tens of thousands of Vietnamese temporarily out of work.

"I think this will hurt Vietnam's economy and affect the rest of the world as these Taiwanese companies are taking international orders," she warned. "It will also hurt Vietnam's image and deter new investors from coming to Vietnam."

Taiwan is Vietnam's fourth biggest foreign investor after Japan, South Korea, and Singapore, with Taiwanese companies plunging $27.3 billion into the communist country from 1988 to 2014.

Vietnam, like many countries, officially recognises China over Taiwan -- a self-governing island which Beijing views as part of its territory awaiting reunification.