Beijing recorded its highest number of new Covid-19 cases for a year and a half on Sunday, as the Chinese capital gears up to host the Winter Olympics in five days.

China will hold the Games in a strict "closed-loop" bubble as part of its zero-Covid strategy of targeted lockdowns, border restrictions and lengthy quarantines.

The approach has helped the world's second-largest economy keep the number of new infections far lower than many other countries, but it is battling local outbreaks in several cities as well as in the Olympic bubble.

The upcoming Lunar New Year -- China's biggest national holiday -- presents further challenges as millions of people return to their hometowns and mingle with family and friends.

Beijing's tally of 20 new cases on Sunday was the city's highest since June 2020, according to the National Health Commission (NHC).

City authorities have locked down some housing compounds, while officials in Fengtai district -- where most of Sunday's infections were detected -- have begun testing around 2 million people for the virus.

The Olympics bubble separates everyone involved in the Games from the wider Chinese population to curb the risk of infections leaking out.

The estimated 60,000 people inside the bubble are subject to daily testing.

Organisers on Saturday reported 36 cases related to the Games, bringing the total to more than 100 since the bubble was sealed on January 4.

The NHC said Sunday there were 54 new local cases nationwide, as the wealthy eastern city of Hangzhou and the city of Suifenhe in northeastern Heilongjiang province emerged as potential hotspots.

Chinese authorities locked down an area neighbouring Beijing this week following a handful of reported cases, appearing not to publicly announce restrictions that have confined around 1.2 million people in Xiong'an New Area to their homes.