The committee of 16 independent experts had been divided in its conclusion not to declare a global emergency, said Tedros, adding that the decision "should not be taken as a sign that the WHO does not think the situation is serious."
Peter Piot, a professor of global health and director of the London School of Hygiene and Tropical Medicine, said the outbreak was at a critical phase.
"Regardless of the decision not to declare this a Public Health Emergency of International Concern, intensified international collaboration and more resources will be crucial to stopping this outbreak in its tracks," he said. "There cannot be any complacency as to the need for global action."
The biggest tumble in Chinese stocks in more than eight months led global equity markets lower on Thursday as concern mounted about the outbreak.
TRAVEL WARNINGS
In Wuhan, the Hankou railway station was nearly deserted on Thursday, state broadcasts showed. State media reported highway toll booths around Wuhan were closing, effectively cutting off road exits, and all ride-hailing services would be canceled from Friday. Guards were patrolling highways, one resident said.
As the city slipped into isolation, residents thronged hospitals for medical checks and rushed to buy supplies, clearing out supermarket shelves and queuing for petrol.
Other cities were also taking steps to contain the virus.
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Nearby Ezhou shut train stations. Beijing canceled large gatherings, including two Lunar New Year temple fairs, and closed the Forbidden City, the capital's most famous tourist attraction, to visitors until further notice.
The U.S. State Department warned travelers to exercise increased caution in China as airports worldwide stepped up the screening of passengers arriving from the country.
Cases have already been detected in Thailand, Vietnam, Singapore, Japan, South Korea, Taiwan and the United States.
Five people were being tested in Scotland for the virus as a precaution, the BBC reported on Thursday. All had respiratory symptoms and had recently been in Wuhan, it said.
Chinese-ruled Hong Kong, which has two confirmed cases, is turning two holiday camps into quarantine stations as a precaution.
Taiwan has banned anyone from Wuhan from going to the island.
Chinese people had their own ways of protecting themselves.
"I go straight to where I need to go, and then I go home," said 79-year-old Li Meihua, from behind a mask, on the streets of Shanghai.
