A medical member (L) works while another pays a silent tribute to martyrs who died in the fight against the novel coronavirus disease (COVID-19) outbreak and compatriots who died of the disease in Wuhan, central China's Hubei Province, April 4, 2020. (Xinhua/Cai Yang)

An air force helicopter takes off from the Orly Airport in Paris, France on April 3, 2020, to transfer COVID-19 patients to southern France to receive treatment. (Photo by Aurelien Morissard/Xinhua)

Subway passengers pay a silent tribute to martyrs who died in the fight against the novel coronavirus disease (COVID-19) outbreak and compatriots who died of the disease in Beijing, capital of China, April 4, 2020. (Xinhua/Zhang Chenlin)

Aerial photo taken on April 4, 2020 shows the sunset glow in Wuhan, central China's Hubei Province. (Xinhua/Du Huaju)

Air Caraibes aircraft are parked on the tarmac after Orly Airport announced its shutdown, south of Paris, France, April 3, 2020. Paris Orly airport, France's biggest airport for domestic flights, has shut down from March 31 as air traffic dwindles amid the coronavirus pandemic. (Photo by Aurelien Morissard/Xinhua)

People pay a silent tribute to martyrs who died in the fight against the novel coronavirus disease (COVID-19) outbreak and compatriots who died of the disease in Wuhan, central China's Hubei Province, April 4, 2020. (Xinhua/Wang Yuguo)

Aerial photo taken on April 3, 2020 shows the construction site of a hospital for infectious disease in the suburb of Nur-Sultan, Kazakhstan. Kazakhstan is building three hospitals in major cities of Nur-Sultan, Almaty and Shymkent to cope with the COVID-19 epidemic. The hospitals are expected to receive patients in 3-4 weeks. (Photo by Kalizhan Ospanov/Xinhua)

A Chinese national flag flies at half-mast to mourn for martyrs who died in the fight against the novel coronavirus disease (COVID-19) outbreak and compatriots who died of the disease at Tian'anmen Square in Beijing, capital of China, April 4, 2020. (Xinhua/Xing Guangli)

Photo taken on April 3, 2020 shows a man at an empty street in Tehran, Iran. The number of confirmed cases of COVID-19 in Iran reached 55,743 on Saturday, with an increase of 2,560 in the past 24 hours, according to the latest figure from Iran Ministry of Health and Medical Education. (Photo by Ahmad Halabisaz/Xinhua)

A poster shows a Chinese national flag flying at half-mast to mourn for martyrs who died in the fight against the novel coronavirus disease (COVID-19) outbreak and compatriots who died of the disease at Tian'anmen Square in Beijing, capital of China, April 4, 2020. (Xinhua/Xu Xiaoxuan)