BEIJING — Two hospitals have been put under quarantine amid fears of a coronavirus outbreak in China’s capital, with one district reporting an “infection density” second only to Wuhan, the epicenter of the epidemic.

The sudden rise in cases in Beijing this week has people worried both about a potential explosion of infection numbers in the capital and what may happen as millions of Chinese return to work after weeks of relative isolation.

Even the Global Times, a nationalist newspaper affiliated with the ruling Communist Party, described the increase in cases in Beijing this week as “whopping.”

There are 396 confirmed cases of the coronavirus in Beijing, a city of 22 million people. Haidian district has the most, with 61, while the much smaller area of Xicheng has 53, according to Beijing government figures.

The central district of Xicheng — home to the Zhongnanhai compound that houses the offices of the ruling Communist Party’s leaders, many government branches and the central bank — is second to Wuhan in the number of confirmed cases per about a half-square mile, the Global Times reported.

That, along with entirely unconfirmed but persistent rumors in the capital that a senior member of the Communist Party has been infected, has led to speculation that the recent increase in security measures is designed to protect the nomenklatura.

The party is all but certain to decide Monday to postpone the important annual National People’s Congress meeting due to begin March 5 in the Great Hall of the People, across the road from Zhongnanhai.

With migrant workers set to return to Beijing in droves after the coronavirus-related extension of last month’s Lunar New Year holiday, officials are clearly worried about the prospect that the returnees could bring the infection with them. A new rule stipulates that all people entering Beijing must quarantine themselves at home for 14 days before going out in the city.

Now, two hospitals are monitoring hundreds of people for potential infection after a sudden spike in cases.

Fuxing Hospital in the Xicheng district, and only a block away from an apartment complex that is home to many senior government officials, is under a total lockdown.

It reported 36 coronavirus cases Thursday, with eight medical workers and nine cleaning staff infected, as well as 19 patients or their relatives. A total of 668 people who had been in contact with the infected patients were placed under observation.

Six security officers, some of them in People’s Liberation Army-style coats and surgical face masks, came out to stop two Washington Post reporters from approaching.

“The quarantine measures have been there for quite a few days now, and they are enforced on the entire hospital, not just a certain building,” said one of the guards at the main entrance to the hospital, declining to provide his name. “We are not in a position to offer any more information on this matter.”

At the WuMart grocery store some 250 yards away, manager Shi Xiaofen said she was concerned about the spike in new infections at the hospital.

“Everyone in our store has been disconcerted, but there is little we could do other than ensuring disinfection, checking temperatures and reducing human flow to protect our staff and customers,” she said.

Nearby Peking University People’s Hospital, meanwhile, confirmed its first coronavirus infections, news that attracted attention because the hospital was quarantined due to widespread infections during the SARS epidemic in 2003. A total of 164 people who had close contact with them, including medical staff who treated them, are under observation.

Medical workers in full protective gear were guarding the gate Friday, where a sign read that all visitors were banned.

“In order to step up prevention and controls of infections in the hospital, stop the virus from spreading and ensure people’s health and safety, this hospital has decided to close the outpatient department,” a notice said. A separate notice said that visitors were banned from the inpatient department.

The three patients at the hospital are from one family, were discovered Monday to have been infected and were sent to designated treatment centers, Beijing health authorities said at a news conference.

A woman, identified by her surname of Tian, had been hospitalized in the geriatrics department for six months for regular dialysis treatment. Her daughter and son-in-law arrived Jan. 16 in Beijing from Xinjiang and visited her regularly for the following three weeks. Each of them became infected with the virus.

As of Friday, 164 people — 142 other dialysis patients and 22 hospital staff — had been placed under observation. Initial tests all came back negative, but the virus has an incubation period of as long as 14 days.

The hospital has sterilized all areas potentially contaminated by the virus, which scientists have said appears to be able to survive on surfaces, authorities said.

Large parts of the obstetrics department at Beijing Friendship Hospital were closed down after a woman was infected after giving birth there, according to a report from Caixin.

Some residents are taking to social media to complain that it was dangerous to send Beijing doctors and nurses to Wuhan to help treat patients there, saying that this created risks for people who work in or live near the hospital.

“Look at Beijing! The whole country is reporting real numbers but in Beijing, there’s only gossip,” one person wrote on the Weibo social media site, in a post that was deleted by censors. “Does Beijing want to become the second Wuhan?”

Lyric Li and Liu Yang contributed to this report.

Read more: