Fearful they might have contracted the new coronavirus infection, it has told them not to return until February 15, and then only if they fulfill certain criteria.

Duong Tat Thang, Deputy Chairman of Ha Tinh Province, where the company is situated, said there are more than 700 Chinese nationals working in its plant.

During the Lunar New Year holiday 400 of them returned home to China to their families.

Now, Formosa said in a statement, they would have to go through stringent health checks before returning to work. They must be checked and certified by authorities in China that they have been infection-free for more than 14 days. 

When they arrive in Vietnam, they will again have to undergo heath checks. On arrival at the company gates, they would have their body temperature checked again before they are admitted in, the company said.

It has installed devices to check workers' body temperature at all entry and exit points.

The $11-billion Formosa Ha Tinh Steel Corporation in the Vung Ang Economic Zone belongs to conglomerate Formosa Plastics Group.

Elsewhere, authorities in the northern port city of Hai Phong have given companies the option of quarantining workers returning from China for 14 days under the supervision of health officials.

Hai Phong has not reported any cases of infection so far. According to city police, more than 3,000 Chinese workers in the city returned home for the Lunar New Year, including 23 to Wuhan. As of January 28 none of them had reportedly returned.

There are more than 29,000 Chinese workers in Vietnam.

Hanoi, Ho Chi Minh City, Hai Phong, and Khanh Hoa, which account for a majority of them, have not reported how many have returned to Vietnam after the Lunar New Year holiday.

Vietnam has so far recorded five cases of infection, three Vietnamese returning from Wuhan and two Chinese nationals.

As of Friday morning there were 97 suspected cases, with 32 of them in quarantine pending test results.

The government has suspended all flights to and from infected areas in China and suspended visas for visitors from there.

Chinese authorities said 213 people had died of the disease as of Friday morning. More than 9,600 have been infected.

The World Health Organization has declared the outbreak a global public health emergency.