Workers pack medical N95 masks at an aseptic area of a mask production company in Shenyang, capital of northeast China's Liaoning Province, Feb. 8, 2020. For days, the company has pledged continuous work of up to 20 hours per day to ensure the daily output of over 20,000 medical N95 masks, which will be supplied to the novel coronavirus epidemic prevention frontline of Hubei and Liaoning Provinces. (Xinhua/Yao Jianfeng)

Photo shows a medical N95 mask on a production line of a mask production company in Shenyang, capital of northeast China's Liaoning Province, Feb. 8, 2020. For days, the company has pledged continuous work of up to 20 hours per day to ensure the daily output of over 20,000 medical N95 masks, which will be supplied to the novel coronavirus epidemic prevention frontline of Hubei and Liaoning Provinces. (Xinhua/Yao Jianfeng)

A worker checks the quality of medical N95 masks at a workshop of a mask production company in Shenyang, capital of northeast China's Liaoning Province, Feb. 8, 2020. For days, the company has pledged continuous work of up to 20 hours per day to ensure the daily output of over 20,000 medical N95 masks, which will be supplied to the novel coronavirus epidemic prevention frontline of Hubei and Liaoning Provinces. (Xinhua/Yao Jianfeng)

A worker picks out unqualified medical N95 masks at a mask production company in Shenyang, capital of northeast China's Liaoning Province, Feb. 8, 2020. For days, the company has pledged continuous work of up to 20 hours per day to ensure the daily output of over 20,000 medical N95 masks, which will be supplied to the novel coronavirus epidemic prevention frontline of Hubei and Liaoning Provinces. (Xinhua/Yao Jianfeng)

A worker produces medical N95 masks at a mask production company in Shenyang, capital of northeast China's Liaoning Province, Feb. 8, 2020. For days, the company has pledged continuous work of up to 20 hours per day to ensure the daily output of over 20,000 medical N95 masks, which will be supplied to the novel coronavirus epidemic prevention frontline of Hubei and Liaoning Provinces. (Xinhua/Yao Jianfeng)

Workers produce medical N95 masks at a mask production company in Shenyang, capital of northeast China's Liaoning Province, Feb. 8, 2020. For days, the company has pledged continuous work of up to 20 hours per day to ensure the daily output of over 20,000 medical N95 masks, which will be supplied to the novel coronavirus epidemic prevention frontline of Hubei and Liaoning Provinces. (Xinhua/Yao Jianfeng)

A worker packages medical N95 masks at a mask production company in Shenyang, capital of northeast China's Liaoning Province, Feb. 8, 2020. For days, the company has pledged continuous work of up to 20 hours per day to ensure the daily output of over 20,000 medical N95 masks, which will be supplied to the novel coronavirus epidemic prevention frontline of Hubei and Liaoning Provinces. (Xinhua/Yao Jianfeng)

Workers produce medical N95 masks at aseptic areas of a mask production company in Shenyang, capital of northeast China's Liaoning Province, Feb. 8, 2020. For days, the company has pledged continuous work of up to 20 hours per day to ensure the daily output of over 20,000 medical N95 masks, which will be supplied to the novel coronavirus epidemic prevention frontline of Hubei and Liaoning Provinces. (Xinhua/Yao Jianfeng)

A worker packages medical N95 masks at a mask production company in Shenyang, capital of northeast China's Liaoning Province, Feb. 8, 2020. For days, the company has pledged continuous work of up to 20 hours per day to ensure the daily output of over 20,000 medical N95 masks, which will be supplied to the novel coronavirus epidemic prevention frontline of Hubei and Liaoning Provinces. (Xinhua/Yao Jianfeng)