The Blood Center of Shandong Province, the second most populous in China, issued red alert warnings for insufficient inventory for two blood types in recent days, China National Radio reported as quoted by Bloomberg.

Fewer people went on the streets due to the Covid situation and the cold weather, while early holidays at universities also reduced the pool of student donors, the state-owned media said, citing officials.

Red alert is the highest level of warning, which means the blood in store can only meet the dosage of acute and critically ill patients for three days, the newspaper reported.

The Health Commission of Suzhou city in the eastern province of Anhui called for voluntary blood donation in a Dec 20 statement on its official website.

The Covid pandemic posed an “enormous challenge” to blood collection, resulting in tightness of supply in medical treatment, the statement said as quoted by Bloomberg.

China might have witnessed 248 million people, or nearly 18 percent of the total population, contracting COVID-19 during the first 20 days of December, a leaked document has shown.

Nearly 37 million people in China may have been infected with Covid-19 on a single day this week, according to estimates from the government’s top health authority, reports Bloomberg News.