Police reinforcements have been sent to maintain a coronavirus quarantine on a tower block in the German city of Göttingen after violence on Saturday.
Seven-hundred people were placed in quarantine, but about 200 who attempted to get out clashed with police.
Residents - now fenced off - attacked police with fireworks, bottles and metal bars, officials said.
The quarantine was imposed on Thursday, after two residents tested positive, then more tests showed 102 infections.
At that point the infection rate there had risen to a critical level of 44.8 per 100,000 inhabitants across seven days - the national threshold for containment of the virus is 50 new infections per 100,000.
Local authorities in Germany have flexibility to impose rules for their area, which differ regionally.
By Friday, 120 people were found to be infected. Most residents have been complying with the quarantine.
Eight police officers were injured in Saturday's violence and a suspect was detained, but released after questioning.
Anyone within the block who tests negative has to have a further test. If that is also negative, they will be allowed to leave the block, but under certain conditions, such as wearing a mask.
Local officials cited communication problems, with many of the residents not understanding the need for a second test.
Translators have been used and information in German and Romanian is now being texted to those who need it, German media report.
Göttingen officials say there is overcrowding among the block's poor residents: the flats are only 19 to 39 sq m (205 to 420 sq ft) in size and some families have four children.
Hotspots push up German R number
In another development, Germany's reproduction (R) number has risen to 2.88 - the number of people who someone with Covid-19 could infect. A number below one is seen as necessary to contain the spread of the disease.
The Robert Koch Institute issued the data based on a four-day average. The seven-day average came up with a lower figure of 2.03.
The institute cited isolated outbreaks, such as the Tönnies meat processing plant in Gütersloh district, North Rhine-Westphalia, for the rise.
So far there is no sign that Germany is seeing a second wave of Covid-19, the BBC's Damien McGuinness reports from Berlin. As Germany's overall infection rate is low, these sudden local outbreaks have a big impact on the national R number.
In the past week, 140 local authorities have seen no new cases at all.
Germany is generally considered to have done a good job containing the virus, thanks to widespread testing. The latest confirmed figures show 189,949 people testing positive, and 8,889 deaths - significantly lower than similar sized European neighbours.
The localised outbreaks - such as the Göttingen apartments and Tönnies - have been contained so far and have been attributed to poor living and working conditions.
Because of the Tönnies case the Gütersloh area has risen above 50 new infections per 100,000 inhabitants over seven days - over the limit set by the German authorities to contain the virus.
Meat plant infections
Covid-19 cases have continued to rise at the Tönnies slaughterhouse.
The number of positive tests linked to the plant in western Germany has risen to 1,331 - more than 20% of the workforce. The Gütersloh authorities told the 6,500 employees and their families to go into quarantine last week.
The prime minister of North-Rhine-Westphalia, Armin Laschet, warned of "an enormous risk of pandemic", while conceding that the outbreak was currently confined to Tönnies and could still be dealt with through a targeted lockdown.
German slaughterhouses employ many foreign workers, and the local authorities are trying to arrange Polish, Bulgarian and Romanian translators to explain the need for restrictions.
The outbreak there has fuelled calls in Germany for improving working conditions at slaughterhouses, as Covid-19 infections have also occurred at other meat plants.