The World Health Organization (WHO) declared coronavirus a global emergency.
The United States reported its first case of person-to-person transmission of a fast-spreading new coronavirus on Thursday.
The vast majority of the more than 8,100 cases detected globally, according to the latest official data, have been in China, where the virus originated in an illegal wildlife market in the city of Wuhan.
But more than 100 cases have emerged in other countries, from Japan to the United States, spurring cuts to travel, outbreaks of anti-China sentiment in some places and a surge in demand for protective face masks.
"There's only so much we can do," said an official at Kukje Pharma Co <002720.KS>, a South Korean firm considering doubling or tripling shifts to cope with a rush of orders for "tens of millions" of masks.
Officials from the U.S. Centers for Disease Control and Prevention said in a conference call that the flu-like virus was confirmed in a man in Illinois, bringing the total number of U.S. cases to six. The man's wife, who was also infected, had previously travelled to China, but he had not.
Experts say cases of person-to-person transmission outside China are especially concerning because they suggest greater potential for the virus to spread further.
The total number of infections in a health crisis that is forecast to sharply dent China's economy, the world's second-largest, has already surpassed the total in the 2002-2003 Severe Acute Respiratory Syndrome (SARS) epidemic.