Patients from Germany, Japan, Taiwan and Vietnam have been diagnosed with the new coronavirus without having visited China, health officials said during a World Health Organization news conference Wednesday.
Human-to-human transmission outside of China "worries us," said Tedros Adhanom Ghebreyesus, director general at WHO.
Partly because of human-to-human transmission outside of China and partly because of a continued increase in cases, the WHO said it will reconvene on Thursday to determine whether to declare coronavirus a public health emergency of international concern.
The committee deliberated for two days last week, but ultimately decided against it.
Still, Tedros stressed, the vast majority of reported coronavirus cases, roughly 99% of the more than 7,700, have been in China.
Among those, 20% have been severe and 2% have been fatal. All 170 deaths have been in China.
WHO will send a group of international experts to work with the Chinese experts on the ground to develop a better understanding of the new coronavirus' severity and infectiousness.
While there is no treatment or vaccine so far, scientists in Australia became the first outside of China to grow the new coronavirus in a laboratory. Sharing that data should make it easier for researchers around the world to develop diagnostic tests, drugs and vaccines.
In the meantime, airlines around the world have suspended routes to China.
American Airlines announced that it would suspend two such routes on Wednesday, citing "significant decline in demand for travel to and from China."
Flights from Los Angeles International Airport to Shanghai Pudong Airport and to Beijing Capital International Airport will not run from Feb. 9 through March 27, the company said in a statement.
The United Kingdom's national airline, which operates daily flights from London to Shanghai and Beijing, said it made the decision "following advice from the Foreign Office against all but essential travel."
"We apologize to customers for the inconvenience, but the safety of our customers and crew is always our priority," British Airways said in a statement Wednesday. "Customers due to travel to or from China in the coming days can find more information on ba.com."
South Korean low-cost carrier Air Seoul and Indonesian budget airline Lion Air have also suspended flights to mainland China, while several other airlines have reduced the number of flights to the country.
Other airlines suspending flights include Lufthansa Group, Cathay Pacific, Finnair, Air Asia, Air India, Air Canada, All Nippon Airways, Asiana Airlines and Korean Air.
The epicenter of the deadly outbreak is in Hubei province's sprawling capital, Wuhan, which authorities have placed on lockdown in an effort to stop the spread of infection.
Hong Kong leader Carrie Lam announced at a press conference Tuesday that train service to mainland China will be halted, starting at midnight Thursday. Lam said two train stations connecting the semi-autonomous Chinese city to the mainland also would be closed and some flights would be canceled.
The new coronovirus causes symptoms similar to pneumonia that can range from mild, such as a slight cough, to more severe, including fever and difficulty breathing, according to the U.S. Centers for Disease Control and Prevention.
The disease has already spread overseas with cases confirmed in over a dozen other countries, including five in the United States.
A growing number of companies, including American firms, are evacuating staff from China or restricting travel there amid the health crisis.
The U.S. Consulate in Wuhan will evacuate its staff along with their families and some other Americans on Wednesday morning, a spokesperson for the U.S. Department of State told ABC News. That chartered flight will travel to California's Ontario International Airport, where everyone on board will be screened for symptoms at the airport prior to leaving. They'll also be subject to additional screening, observation and monitoring requirements by the CDC.
The U.S. Department of State issued a new travel advisory on Monday urging Americans to reconsider traveling to any part of China due to the disease, rather than just to Wuhan and other affected areas. U.S. citizens are advised not to travel to Hubei province.
ABC News' Joseph Simonetti and Mina Kaji contributed to this report.