Thousands of containers of frozen pork, chicken and beef are piling up at some major Chinese ports as transport disruptions and labor shortages slow operations, people familiar with the matter said.

Deliveries are mounting at ports including Tianjin, Shanghai and Ningbo because there aren’t enough truck drivers to collect containers due to travel curbs imposed in the country to control the coronavirus, said the people, who asked not to be identified because they’re not authorized to speak publicly.

Ports are also starting to run out of electricity points to freeze the containers and some ships have been told to reroute to other destinations in mainland China and Hong Kong, the people said.

China is a massive importer of meat from South America, Europe and also the U.S., and has been boosting purchases to help ease shortages caused by African swine fever. The country increased imports of meat and offal by almost 50% in 2019 to a record of about 6.2 million tons, customs data show.

It remains unclear when port operations will return to normal as truck drivers returning from other cities are quarantined for 14 days and other transport restrictions on trucks remain in place, the people said.

The government encouraged factories to ramp up production this week after extended New Year holidays. Outbreaks of the virus have sickened more than 70,000 and killed over 1,800 in China. More than 220 million migrant workers have not returned on time and may travel in late February or March, Liu Xiaoming, the transport minister, said on Saturday.

The office of the spokesman for the General Administration of Customs in Beijing did not answer phone calls seeking comment.