China has recorded its highest number of daily new coronavirus cases in almost six weeks, sparking fears of a second wave of Covid-19 after restrictions were eased.

Officials say the sudden rise is due to infected travellers arriving from abroad, many of them crossing the border from Russia.

A total of 108 new coronavirus cases were reported in mainland China on Sunday, up from 99 a day earlier and marking the highest number of cases since 143 infections were reported on March 5.

Heilongjiang province, which borders Russia in the north-east, has become China's new battleground against Covid-19 as the rise threatens to push the entire country back into a state of near paralysis.

The National Health Commission said 98 of the new cases - or more than 90 per cent - were imported, a new record.

A total of 49 Chinese nationals who entered Heilongjiang province from Russia tested positive.

"Our little town here, we thought it was the safest place," said a resident of the border city of Suifenhe, who only gave his surname as Zhu.

"Some Chinese citizens they want to come back, but it's not very sensible, what are you doing coming here for?"