Countries across Europe that had appeared to be beating back coronavirus outbreaks are suffering from rising cases as they open up their economies.
Germany, Czech Republic and Slovakia all saw rising numbers of cases and are considering delaying measures to ease lockdown orders.
UK tourists in Croatia and Austria raced home to beat new quarantine orders imposed at short notice on the back of rising case numbers.
Germany recorded its highest number of coronavirus cases in more than four months, as infections rose to 2,034 in the 24 hours ending on Saturday morning.
About 40 schools in Berlin have confirmed infections in the two weeks since reopening. Another prime suspect for the new cases are tourists returning from holidays abroad.
"Some of the infection figures come from holidaymakers returning, but then also from partygoers and people who obviously no longer comply with protection regulations," said Stephan von Dassel, mayor of a district in central Berlin.
Chancellor Angela Merkel has ruled out any further easing of restrictions in place to combat the virus. Germany is “still in the middle of a pandemic”, she said.
Czech authorities are reintroducing compulsory face masks on public transport, but so far has not made the coverings mandatory in other enclosed spaces like restaurants and shops.
The Czech government was among the first in Europe to introduce curbs on movement and business as the outbreak took hold, and was widely praised for limiting its toll.
On Friday, it reported 506 new coronavirus cases in the previous 24 hours, the highest number of new infections in one day, and 19 of the 411 deaths have been in the last week.
Slovakia reported 123 new cases of the coronavirus on Friday, its highest daily number since the pandemic reached the country in March, and 91 new cases on Saturday.
Friday was the third time the country announced more than 100 new cases in a single day. It has reported 3,316 cases and 33 deaths.