Open this photo in gallery People wearing face masks ride an escalator at a shopping area in Beijing on April 6, 2020. TINGSHU WANG/Reuters

Mainland China reported on Tuesday a decline in imported coronavirus cases, after closing its borders to virtually all foreigners, while increasing vigilance on infected people who show no symptoms but can still pass on the virus.

Mainland China had 32 new confirmed cases of the coronavirus on Monday, down from 39 cases a day earlier, the National Health Commission said.

All of the 32 confirmed cases involved travelers arriving from overseas, compared with 38 imported cases a day earlier. The overall number of imported infections so far stands at 983, the health authority said.

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Imported cases and asymptomatic patients have become China’s chief concern after draconian containment measures succeeded in slashing the overall infection rate.

China has shut its borders to foreigners as the virus spread globally, though most imported cases have involved Chinese nationals returning from overseas. International flights have been slashed to around 3,000 a day in April from the tens of thousands previously.

It has also started testing all international arrivals for the virus this month.

The total number of confirmed cases in mainland China stood at 81,740 as of Monday, according to the authority.

China reported 30 new asymptomatic cases on Monday, nine of which involved incoming travelers. Of the new asymptomatic cases, 18 were in central Hubei province.

As of Monday, 1,033 asymptomatic patients were under medical observation.

The National Health Commission reported no new deaths in Wuhan, capital of Hubei and epicenter of the outbreak in China, for the first time since the outbreak started.

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Wuhan is due to allow people to leave the city on Wednesday for the first time since it was locked down on Jan. 23 to curb the spread of the epidemic.

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