Beijing has closed around 10% of the stations in its vast subway system as an additional measure against the spread of coronavirus.

The subway authority, in a brief message, said only that the decision to shut 40 stations was taken as part of epidemic control measures. No date for the resumption of full services was given.

Beijing has been on high alert over the spread of Covid-19, with restaurants and bars limited to takeout only, gyms closed and classes suspended indefinitely.

Major tourist sites in the city, including the Forbidden City and Beijing Zoo, have closed their indoor exhibition halls and are operating at only partial capacity.

A few communities where cases were discovered have been isolated. People residing in "controlled" areas have been told to stay within city limits, including 12 areas deemed high-risk and another 35 considered medium-risk.

City residents are required to undergo three tests throughout the week as authorities seek to detect and isolate cases without imposing the sort of sweeping lockdowns seen in Shanghai and elsewhere. A negative test result obtained within the previous 48 hours is required to gain entry to most public spaces.

Beijing on Wednesday recorded just 51 new cases, five of them asymptomatic.

The subway closures should have relatively little impact on city life, with China observing the Labour Day holiday this week and many commuters in the city of 21 million already working from home.

In one downtown neighbourhood categorised as high-risk on Wednesday, the streets were practically deserted apart from a few delivery drivers on scooters and the occasional pedestrian and car.

All businesses were shut except for supermarkets and fruit and vegetable stores. Outsiders generally avoid high-risk areas to avoid the possibility of their presence registering on the tracing apps installed on virtually all mobile phones, creating potential problems for future access to public areas.

While taking a lighter touch in Beijing, China has overall stuck to its strict "zero-Covid" approach that restricts travel, tests entire cities and sets up sprawling facilities to try to isolate every infected person. Lockdowns start with buildings and neighbourhoods but become city-wide if the virus spreads widely.

That has caused the most disruption in Shanghai, where authorities are slowly easing restrictions that have confined most of the city's 26 million people to their homes, housing compounds or immediate neighbourhoods for close to a month, and in some cases longer.

Shanghai reported another 4,982 cases on Wednesday, all but 260 of them asymptomatic, along with an additional 16 deaths. That continues a steady decline in China's largest city which recorded a daily peak of 27,605 new cases nearly three weeks ago on April 13.

The surprisingly low death toll amid an outbreak of more than 400,000 cases in the city that is home to China's main stock market and biggest port has sparked questions about how such deaths are tallied.

The rigid and widely derided restrictions have led to shortages of food and medical aid along with a wider - though likely temporary - impact on the national economy.

Desperate, outraged citizens have confronted authorities at barricades and online, screamed out of their windows and banged pots and pans in a sign of their frustration and anger.