More than 1,200 flights going in and out of Beijing have been canceled as a new coronavirus outbreak in China’s capital grows.

The number of confirmed cases of the illness in Beijing reached at least 137 this week, a dramatic increase after months of no reported cases, according to the New York Post. The city has closed all schools and 11 markets in an attempt to stop a potentially enormous explosion of cases in the densely populated city of 22 million.

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