WHO spokesman Chris Lindmeier warned that closing borders could in fact accelerate its spread, with travelers entering countries unofficially.
“As we know from other scenarios, be it Ebola or other cases, whenever people want to travel, they will. And if the official paths are not opened, they will find unofficial paths,” he said.
He said the best way to track the virus was at official border crossings.
Meanwhile in Wuhan, voluntary evacuations of hundreds of foreign nationals are under way.
The UK, Australia, South Korea, Singapore and New Zealand are expected to quarantine all evacuees for two weeks to monitor them for symptoms and avoid contagion
Estimates by the University of Hong Kong suggest the true total number of cases could be far higher than official figures suggest. Based on mathematical models of the outbreak, experts in Wuhan say more than 75,000 people may have been infected in the city of Wuhan alone, where the virus first emerged.
Most cases outside China involve people who have been to Wuhan. But Germany, Japan, Vietnam, the US, Thailand and South Korea have reported person-to-person cases – patients being infected by people who had travelled to China.