A northeastern Chinese city has partially shut its borders and cut off transport links after the emergence of a local coronavirus cluster that has fuelled growing fears of a second wave of infections in China.

Jilin, with a population of more than four million, suspended bus services on Wednesday and said it will only allow residents to leave the city if they have tested negative for Covid-19 in the past 48 hours and complete an unspecified period of "strict self-isolation".

All cinemas, indoor gyms, internet cafes and other enclosed entertainment venues must shut immediately, and pharmacies must report all sales of fever and antiviral medicines, the local government said in a statement.

The city is located in the eponymous province of Jilin.

A cluster of infections was reported in the suburb of Shulan over the weekend, with Jilin's vice mayor warning on Wednesday that the situation was "extremely severe and complicated" and "there is major risk of further spread".

The city reported six new cases on Wednesday, all linked to the Shulan cluster, bringing the total number of cases linked to a local laundry worker to 21.

Shulan shut down public transportation as well as trains leaving the city on Sunday.

Jilin city, the second-largest in Jilin province, also suspended train services from its main railway station Wednesday morning, state broadcaster CCTV reported.

China has largely brought the virus under control, but it has been on edge about a potential second wave as it has lifted lockdowns and restrictions across the country.

The emergence of new cases in Wuhan in recent days, after weeks without fresh infections, has prompted a campaign to test all 11 million residents in the city where Covid-19 first emerged late last year.