Wuhan is ground zero of the pneumonia outbreak that has spread across China and Thailand since December.

Their blood samples were sent to the Nha Trang Pasteur Institute to determine the cause of the fever. A list of people who have been in close proximity to the two has also been compiled for further monitoring.

The two are a 22-year-old man and a three-year-old boy who traveled in the same tour group.

By 7 a.m. on Wednesday, the two's temperatures have cooled down to normal ranges. Their test results also came back normal.

This is the first case of sick foreigners entering Vietnam since the acute pneumonia outbreak in China.

Airports in Hanoi, Ho Chi Minh City and Khanh Hoa Province, a major destination for Chinese tourists, have installed equipment to monitor arriving passengers’ body temperature.

The disease, possibly caused by a newly emerging strain of the coronavirus family that caused SARS (Severe Acute Respiratory Syndrome) and MERS (Middle East Respiratory Syndrome), earlier this month infected a Chinese woman in Thailand, who has since been quarantined, the first time the virus has been spotted outside China, newswire Reuters reported.

"From the information that we have it is possible that there is limited human-to-human transmission, potentially among families, but it is very clear right now that we have no sustained human-to-human transmission," Maria Van Kerkhove, acting head of the World Health Organization’s emerging diseases unit, has said.

There is no specific treatment for the new virus, but anti-virals are being considered and could be "re-purposed", she added.

Forty one cases have been detected in Wuhan, with a 61-year-old man dying of the illness, Chinese authorities said.

The Vietnamese Ministry of Health has warned people to keep their distance from people with acute respiratory infections and wear a mask when talking to them.

Keeping bodies warm and maintaining personal hygiene, especially cleaning hands regularly with soap and gargling with antiseptic rinse, are also recommended.

People coming from Wuhan with signs like fever, coughing or difficulty to breath should go the nearest medical facility, the ministry said.