Three cases of coronavirus have been confirmed in areas just outside Beijing, with fears the virus may have spread through frozen food.
A total of 158 cases have been reported across the city since a new cluster of infections linked to its sprawling Xinfadi wholesale market was detected last week.
Twenty-one cases were confirmed on Thursday, with another in the neighbouring city of Tianjin and two more in the Hebei province that surrounds Beijing.
The case in Tianjin involves a 22-year-old man who works in the city's Conrad Hotel washing dishes and occasionally cleaning frozen seafood, China's Global Times reported.
He had not travelled prior to developing symptoms and had had no known contact with any suspected cases, leading experts to suspect he may have picked up the disease by touching contaminated food.
He could have been infected by handling the food or even the ice used to freeze it, Yang Zhanqiu, a virologist at Wuhan University, told the outlet.
"For example, at -20C to -30C environment, the virus could live for months or even years," he said.
"The frozen seafood touched by the Tianjin patient could be of the same batch with those shipped to Beijing Xinfadi."
Yang told the paper people should avoid eating raw food and be cautious when consuming processed frozen food.
Chinese health officials say the virus was found on a chopping block used to cut up imported salmon at the Xinfadi market, which supplies more than 70 per cent of Beijing's fresh produce.
The news sparked panic among restaurateurs and retailers who immediately cancelled their orders and stopped selling the fish. Large supermarket chains, including Wumart and Carrefour, also removed it from their shelves.
But Shi Guoqing, the deputy director of China's Centre for Disease Control and Prevention (CDC), said there was "no evidence" salmon was the immediate source of the outbreak.
"We currently have no evidence that salmon is a carrier or an intermediate carrier of the coronavirus," he said at a press conference on Tuesday.
"In the contaminated area of Xinfadi Market related to this new outbreak, there is indeed salmon product found to be contaminated. But no virus has been detected on the salmon product that has not yet entered the contaminated area."
Wu Zunyou, a chief epidemiologist with the CDC, suggested wet markets were emerging as hot spots for the virus because much of the fresh produce, including seafood, was stored in low temperatures and wet conditions that helps the virus to survive.
He said a high number of infections had also broken out among sellers of beef and mutton.
People infected with the virus have now been banned from leaving Beijing, along with anyone who they've had close contact with, according to the Global Times.
Close contacts of the Xinfadi market and residents of "high or medium risk residential compounds" have also been prohibited from leaving the city, the newspaper said.
All those who have recently visited the market, or been in close contact with a merchant, have been asked to quarantine for 14 days, while testing is being rolled out to local restaurant owners, farmers' market vendors and canteen workers.
Beijing is now collecting around 400,000 swabs a day amid fears the new outbreak could trigger a second wave of the virus.
"I had wanted to get tested anyway, but my workplace said all mall staff must be tested," a 25-year-old shop assistant surnamed Pang told the AFP news agency, as she lined up at the Workers' Stadium in central Beijing to be swabbed.
"I don't really mind waiting, it's for the greater good and the benefit of society."
A chef from a nearby restaurant, who gave his surname as Wang, said he had been sent by his boss to get tested.
"Anyway we haven't had many customers over the past few days, people are scared to go out as much now," he said.