Thousands of migrants were left without shelter on Wednesday after overnight fires gutted their overcrowded camp on the Greek island of Lesbos, and authorities warned that some asylum seekers who tested positive for Covid-19 could spread the virus.

The Moria camp, which hosts more than 12,000 people, was “probably totally destroyed”, one Greek migration official said. Athens declared a state of emergency on Lesbos.

As migrants camped out in fields nearby or sifted through smouldering debris in search of possessions, deputy migration minister George Koumoutsakos said about 3,000 people affected by the fires would be housed in tents.

“The situation in Moria cannot go on (as it is) because it is simultaneously a public health and national security issue,” Prime Minister Kyriakos Mitsotakis said in a televised address, adding that managing migrant flows was a “European problem”.

The cause of the fires, which broke out soon after midnight, remained unclear but authorities were investigating whether they were started deliberately after Covid-19 tests led to the isolation of a number of refugees.

“There was not just one but many fires in the camp. Migrants threw stones at firefighters trying to put out the fires,” Constantine Theophilopoulos, fire brigade chief for the northern Aegean, told ERT TV.