Germany’s public health boss has said he is “very concerned” by the rising number of coronavirus infections in the country.
Countries across Europe are grappling with increasing numbers of new infections and the problem of holidaymakers travelling for their summer holidays.
Lothar Wieler, head of the Robert Koch Institute (RKI), sad Germans had become "negligent" and reminded people to following the social distancing rules in place.
He said the country must stop Covid-19 once again spreading "rapidly and uncontrollably”.
Mr Wieler said: ”We don't know yet if this is the beginning of a second wave but of course it could be.”
It comes after the UK’s prime minister Boris Johnson warned that Europe was suffering the symptoms of a second coronavirus wave.
Mr Johnson hinted that quarantine restrictions could be imposed on further countries if a Covid-19 resurgence hits the Continent.
In the past week Germany has recorded 3,611 new infections.
It on Tuesday issued a travel warning for three regions in Spain, Aragón, Catalonia and Navarra, all of which have seen a spike in Covid-19 infections.
The UK imposed a 14-day quarantine on all arrivals from Spain - a move Spanish Prime Minister Pedro Sánchez said was not justified.
Mr Wieler asked people for the first time to wear a mask outdoors if they cannot maintain a physical distance of at least 1.5 metres. The guidance had previously been to wear masks indoors in public.
