About 5 million people left Wuhan, China, before the lockdown last week, the city's mayor said Sunday.

As of Monday, 81 people have died from Wuhan coronavirus, and more than 2,700 cases have been reported in mainland China.

The virus has spread to 13 countries as well, with five confirmed cases in the US.

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The mayor of Wuhan, China, said about five million people left the city before it was placed on lockdown last week to slow the spread of coronavirus.

Mayor Zhou Xianwang said about 9 million people remained in the city after the quarantine started on Thursday, according to the South China Morning Post. Wuhan is the seventh-largest city in China with a population of about 11 million.

Escaping the outbreak may have been the cause for some people fleeing the city. But it also coincided with the Lunar New Year, China's most important holiday in which city workers return to their hometowns.

Lunar New Year is the largest annual human migration, with Chinese citizens making a combined 3 billion trips during the season.

Chinese workers get a week off work, from January 24-30. For many, it's the only time they get to go home during the year, which may explain the desperation to leave Wuhan in the face of an impending quarantine.

It appears that Chinese officials have sympathized, since the holiday has officially been extended to February 2.

As of Monday, Chinese officials confirmed that 81 people have died from Wuhan coronavirus, and that 2,744 people are currently infected on mainland China, with an additional 13 cases in Hong Kong and Macao.

The virus has also spread to 13 other countries, including the US, where there are five cases as of Monday afternoon.