The premier of the western German state of North Rhine-Westphalia said on Tuesday he was putting the Guetersloh area back into lockdown until June 30 after a coronavirus outbreak at a meatpacking plant there.
Guetersloh is the first area in Germany to go back into lockdown after the authorities began gradually lifting restrictive measures at the end of April.
State premier Armin Laschet, who had led calls for Germany to ease lockdown measures, said bars, museums, galleries, cinemas, sports halls, gyms and swimming pools in Guetersloh would be closed, and picnics and barbeques prohibited.
About 360,000 people live in Guetersloh.
"This is a limited measure of caution. We will lift the measure as soon as possible, when we have certainty about the safety of the infection," Laschet told a news conference. "It is a preventative measure."
More than 1,500 workers at a meat processing plant in Guetersloh had tested positive for the coronavirus, plus some of their family members and 24 people who had no connection to the plant, he said.
Laschet is a leading contender to succeed Chancellor Angela Merkel when her fourth term in office expires next year. Further outbreaks of the virus in his state, Germany's most populous, could damage his chances.
Earlier on Tuesday, the head of the Robert Koch Institute for public health, Lothar Wieler, said the coronavirus reproduction rate in Germany is currently estimated at 2.76, probably mainly due to local outbreaks.
A reproduction rate, or 'R', of 2.76 means that 100 people who contracted the virus infect, on average, 276 others.
Wieler said Germany is at risk of a second coronavirus wave but added he was optimistic it could be prevented.