China reported 63 new Covid-19 infections on Thursday -- the highest single-day tally since July -- as authorities try to stamp out an outbreak of the virus in a city of 11 million near Beijing.

The virus first emerged in central China in late 2019, but since then authorities have largely brought the situation under control through travel restrictions, strict lockdowns and mass testing.

But a recent outbreak in northern Hebei province, which surrounds Beijing, has seen cases spike and prompted mass testing, school closures and travel links being cut into the province.

On Thursday, there were 51 more cases reported in the province, the National Health Commission reported -- plus another 69 asymptomatic cases.

State broadcaster CCTV showed a small crowd gathered outside a railway station in Shijiazhuang being directed by medical staff in full hazmat suits and protective wear.

"I did the nucleic acid test last night, but don't have the results yet. Without it I can't leave the city," one young woman told CCTV.

Major highways leading into the city of Shijiazhuang, around 300 kilometres (200 miles) south of Beijing, have been closed and inter-city bus travel halted in an attempt to prevent the virus spreading beyond the city.

The state-run Global Times reported that railway tickets from Hebei to the capital Beijing were no longer being sold in a bid to halt the spread of the virus.

One district in Shijiazhuang -- which has a population of 11 million -- has been declared high risk and sealed off, and authorities said tens of thousands have already been tested for the virus.

There were also 11 imported cases and one other domestic case in northeastern China confirmed Thursday.