Chinese officials and the World Health Organization (WHO) are trying to contain an outbreak of pneumonia in the central Chinese city of Wuhan.
Health experts suspect that the pneumonia cases could be linked to a new form of coronavirus. The virus is blamed for at least one death.
The WHO has said there may have been limited human-to-human transmission of the virus within families.
Chinese officials say a seafood market in Wuhan is thought to be at the center of the outbreak. Officials said one woman may have gotten the virus from her husband, who worked at the market. The two are among 41 people shown to have pneumonia thought to be caused by the virus.
Officials said some of the sick have denied visiting the market.
The outbreak comes two weeks before the start of the Lunar New Year holiday, when many of China's 1.4 billion people will be traveling to their hometowns or overseas.
WHO and Chinese officials are taking steps to ensure the disease does not spread.
The officials in Wuhan confirmed that Thailand has quarantined a Chinese woman. It is the first case of the mystery strain of coronavirus to be found outside of China. The woman is said to have come from Wuhan.
The coronavirus is from a family of viruses that can cause both the common cold and more serious diseases.
On Wednesday, a Hong Kong health official told reporters that the threat of human-to-human transmission remains low. Chuang Shuk-kwan said that doctors and hundreds of other people have been in close contact with infected individuals and have not been infected themselves. She spoke to reporters after returning from a visit to Wuhan.
With the Lunar New Year set to begin on January 25, the WHO called on Thai officials and the public to be on guard against the virus. Thai health officials announced Wednesday they were increasing security at airports.
The United States released a warning about the latest outbreak for American citizens in China.
I'm Susan Shand.