LESBOS, Greece — They’ve been sleeping on tombstones and on the side of the road, in parking lots and among dried weeds on the hillsides. They’ve pitched makeshift tents with bamboo poles and blankets. They’ve used the few clothes they have to make mattresses so their babies don’t sleep on tarmac.

About 4,000 children, including hundreds of infants, and 8,000 adults have been stranded without shelter or sanitation on the Greek island of Lesbos, most of them packed along a 1.5-mile stretch of coastal road, since blazes last week razed their squalid refugee camp, Europe’s largest.

“We escaped from fire, but everything is black,” said Mujtaba Saber, sitting on a thin blanket spread on a street, next to his napping three-year-old son. His 20-day-old baby slept nearby in her mother’s arms.

The fires have intensified what was already a humanitarian disaster on the Aegean islands, where Europe warehouses tens of thousands of migrants in overcrowded camps with severe shortages of toilets, showers, medical care and even food.

The camps are a centerpiece of the European Union’s strategy, following the migrant crisis of 2015-16, to slow the movement of people from the Middle East, Asia and Africa who try to reach Europe. The now-destroyed camp, called Moria after a nearby village, had for years been a byword for misery, an unflattering emblem of European policy.

The razing of the camp “was a tragedy,” Prime Minister Kyriakos Mitsotakis of Greece said in a speech on Sunday. “It was a warning bell to all to become sensitized. Europe cannot afford a second failure on the migration issue.”

Displaced mothers with their children in a field near the beach on Lesbos on Saturday.

Aid workers and Greek officials say the fires were started by a small group of asylum seekers who were angry that the government had instructed them to quarantine after an outbreak of coronavirus, and put the entire camp under a lockdown. But if Covid-19 was the spark that lit the tinderbox, its arrival in Moria was hardly a surprise.

The European Commission — the E.U. executive branch that has funded much of the construction and operation of the camps but has not taken responsibility for their squalor — and aid groups had warned that conditions there made Moria an ideal breeding ground for disease outbreaks.

What remains of Moria is a rancid pile of charred tents, ash and debris, melted metal frames, gutted communal toilets and burned rats lying next to potatoes and onions that will never be consumed.