Beijing 2022 organisers said on Monday that the Winter Olympics "face great pressure" because of Covid-19, as China ramps up preparations with a series of test events.

February's Games could be the most restricted mass sporting event since the pandemic began, with no international spectators allowed and a vaccine mandate for anyone entering a strictly enforced "bubble".

Those who have not been vaccinated, including athletes, must quarantine for 21 days on arrival in the Chinese capital before they go into the bubble.

Olympic organisers will trial many of the measures in a series of domestic test events, international competitions and training for overseas athletes that will begin on Friday and last several weeks.

"We expect that over 2,000 overseas athletes, team officials, international technical officials, and timing and scoring professionals will come to China to participate in various competitions," Yao Hui, venue management chief on the Beijing Winter Olympics organising committee, told a briefing.

"We face great pressure in epidemic prevention and control."

China has virtually sealed off its borders to keep Covid infections out. But ahead of the test events it allowed entry to participants that are mainly from Asia, as well as Europe and North America.

For example, athletes from China, South Korea and the Netherlands will participate in the speed-skating test events, officials said. 

Other events cover a variety of sports including skiing, snowboarding, luge, bobsleigh and ice hockey.

They will take place in the three Olympic hubs: Beijing, Yanqing district just outside the capital, and Zhangjiakou in neighbouring Hebei province.

Organisers said they will ensure that test events are carried out using the same arrangements as the Winter Olympics. 

Unlike the Tokyo Olympics, the Beijing Games will have spectators, albeit only people living in mainland China.

But the Winter Olympics bubble will be much stricter than it was in the Japanese capital.

Only fully vaccinated participants, including media and venue staff, can enter the "closed-loop management" bubble without a 21-day quarantine. They cannot leave the bubble for the duration of the Games. 

"From when they enter the bubble to when they leave China, we will strictly enforce full-course point-to-point closed-loop management policies," said Huang Chun, head of epidemic prevention and control on the organising committee.

"In the closed loop, all event participants can only move between the competition venues and participate in activities related to their work, competition, and training. Other activities are not allowed."

The Beijing Olympics, which is facing calls for a boycott from rights groups, is scheduled for February 4-20.

Test events in certain sports were scheduled for last winter but were cancelled due to the pandemic. 

China, where the coronavirus emerged towards the end of 2019, has wrestled down the number of local infections to a trickle by deploying aggressive, mass testing and keeping its borders extremely tight.