A Chinese city of nearly six million people will introduce a wave of coronavirus testing to stamp out a small cluster of cases, authorities said Friday, with state media reporting communities will be locked down.

Since the virus first surfaced in the central city of Wuhan late last year, the country's official number of infections has been restricted to a trickle, mainly among arrivals from abroad. All mass lockdowns have been lifted.

But recent domestic outbreaks have proved the difficulty of stamping out the contagion entirely.

The port city of Dalian in Liaoning province has reported three cases in recent days after going nearly four months without any.

Pedestrians wear face masks in Beijing, China. Authorities in the country had appeared to have the virus largely under control
Pedestrians wear face masks in Beijing, China. Authorities in the country had appeared to have the virus largely under control AFP / GREG BAKER

The fresh outbreak has been linked to a seafood processing company that deals with imported products.

On Friday, the Dalian health commission said the city had to "quickly enter wartime mode, go all-out, mobilise all people and resolutely curb the spread of the epidemic".

It announced strict new measures, including on-the-spot nucleic acid tests for everyone taking the subway line that passes the affected seafood company.

Kindergartens and nurseries have been closed, and some communities have been placed under lockdown, according to state-run newspaper Global Times.

While China appears to have largely brought COVID-19 under control recent domestic outbreaks have proved the difficulty of stamping out the contagion entirely
While China appears to have largely brought COVID-19 under control recent domestic outbreaks have proved the difficulty of stamping out the contagion entirely AFP / STR

City authorities said they would test more than 190,000 people, including employees at shopping malls, wholesale markets and warehouses.

The outbreak comes as hundreds of football players from the Chinese Super League -- which will kick off its much delayed season Saturday -- are in a sealed-off hotel in the city.

The league's 16 teams have been split into two groups for the first games of the drastically rejigged season, with the others to be played in Suzhou, near Shanghai.

The latest cluster has turned the spotlight on the country's food supply chain, and China has banned imports from a number of overseas food producers involved in virus outbreaks.

One Chinese importer told AFP that exporters had earlier been asked to guarantee their shipments were not contaminated.

A document published Thursday by China's State Council also warned that the country's public health system should prepare for a possible second wave of the virus in the winter.

At a press conference earlier this month, officials said samples taken from Whiteleg shrimp packaging in Dalian had tested positive for the virus.

There were 21 coronavirus cases reported in China on Friday, including two of the three recent Dalian cases and 13 in the western region of Xinjiang.

The other six were imported.

Coronavirus China