After weeks with almost no new coronavirus infections, Beijing has recorded dozens of new cases in recent days, all linked to a major wholesale food market, raising concerns about a resurgence of the disease.

The capital is taking steps to try to halt the outbreak, including ramping up testing. On Sunday night Beijing ordered all companies to supervise 14-day home quarantine for employees who have visited the Xinfadi market or been in contact with anyone who has done so.

A restaurant chain selling traditional Beijing noodles shut down a few outlets after two employees tested positive.

There had been almost no new coronavirus cases in the city for two months until an infection was reported on June 12, and since then the total number has climbed to 51, including eight reported in the first seven hours of Sunday.

According to the city’s health authority, contact tracing showed all the infected people had either worked or shopped inside Xinfadi, said to be the largest food market in Asia, or had been in contact with someone who was there.

“Beijing has entered an extraordinary period,” city spokesman Xu Hejian told a news conference on Sunday.

The market was closed before dawn on Saturday and the district containing the market put itself on a “wartime” footing.

The Beijing outbreak has already spread to the neighbouring northeastern province of Liaoning, where the health authority said the two new cases confirmed on Sunday were both people who had been in close contact with confirmed cases in Beijing.

At least 10 Chinese cities, including Harbin and Dalian, have urged residents not to travel to the capital or to report to authorities if they have done so recently.

Huaxiang, a neighbourhood in the same district as the food market and which has one of China’s biggest used car centres, raised its epidemic risk level to high on Sunday, becoming the only neighbourhood in the country to be on high alert.