The World Health Organization (WHO) on Thursday declared a public health emergency of international concern over the outbreak of coronavirus.
"The main reason for this declaration is not because of what is happening in China, but because of what is happening in other countries," said Dr. Tedros Adhanom Ghebreyesus, director-general of the WHO.
"Our greatest concern is the potential for the virus to spread to countries with weaker health systems, and which are ill-prepared to deal with it," he added.
The cases have been centered in China, and the WHO said it has confidence in China's response to the virus.
The declaration, which the WHO previously declined to make, comes as the virus spreads to more countries.
There are now 98 cases in 18 countries outside of China, the organization said, including cases of human-to-human transmission in four countries: Germany, Japan, Vietnam and the United States.
The first person-to-person transmission in the United States was reported Thursday in a person in Chicago who contracted the virus from his spouse who had recently returned from China, but officials said the risk to the general American public remains low.
"We understand this may be concerning, but based on what we know now our assessment remains that the immediate risk to the American public is low," said Centers for Disease Control and Prevention Director Dr. Robert Redfield said earlier Thursday.
There are now 7,834 cases of the virus, almost all of them in China, and 170 people have died, the WHO said.
Despite the declaration, the WHO warned against too many restrictions on travel. Sen. Tom Cotton (R-Ark.) has called for suspending flights from China to the U.S.
"There is no reason for measures that unnecessarily interfere with international travel and trade," Tedros said. "We call on all countries to implement decisions that are evidence-based & consistent."
The spread of the virus has set off concern in Congress, where U.S. health officials held a briefing for all House lawmakers on Thursday.
Rep. Ami Bera (D-Calif.) announced a House Foreign Affairs subcommittee hearing on the virus for next week, the first congressional hearing on the outbreak.