A single coal mine in Poland's Upper Silesia region is behind a record spike in the country's confirmed coronavirus cases, the health ministry says.
Over the weekend 1,151 new infections were recorded nationally.
An outbreak among miners and their families at the Zofiowka colliery in southern Poland accounted for two-thirds of that figure.
The global number of deaths from coronavirus has now passed 400,000. There have been 6.9 million infections.
Poland introduced a strict lockdown early in March, and has avoided the comparatively large number of deaths seen in Western Europe.
In Poland, 1,157 people have died from Covid-19 and 26,561 have been infected but the stubborn persistence of cases in Upper Silesia mean the country has not passed its peak.
Most EU countries recorded fewer new cases than Poland on Sunday.
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Upper Silesia is Poland's industrial heartland with more than a dozen active mines where workers toil in humid conditions at close quarters.
More than 4,000 people in the region have tested positive for the virus. Of Sunday's new infections, 57% were recorded in Upper Silesia.
Coal company JSW says it has reduced output at a mine in Pniowek, and PGG, another company, closed some mines temporarily in May, reports Reuters.
Despite the persistent infections in Upper Silesia, Poland began to ease restrictions on 20 April when parks were allowed to reopen. Some school children returned to school at the end of May.
The spread of infection in confined workplaces has also been seen in mines and factories in South Africa and the US.
Operations at South Africa's Mponeng mine, the world's deepest gold mine, were halted after 164 cases of coronavirus were detected there in late May.
In the US, there have been 20,400 infections in 216 meat processing factories and at least 74 people have died, according to the Midwest Center for Investigative Reporting.