Greece was set Sunday to evacuate hundreds of migrants from a notoriously overpopulated island camp to the mainland.

Two groups, of 142 and 250 "vulnerable" migrants were to board ferries on the island of Lesbos, according to a police source, after leaving the Moria camp where conditions were said to be deplorable. In April, Human Rights Watch urged Greek authorities to act quickly to ward off a potential health crisis in migrant camps lest the coronavirus take hold there.

The sites are battling rampant overcrowding, poor sanitation, lack of proper water supplies and rudimentary healthcare.

A transfer from the Moria camp would be the first since confinement measures were imposed on March 23 to stem the spread of COVID-19.

A few days before that around 600 migrants had been transferred to the Greek mainland.

An estimated 37,000 migrants live in dreadful conditions on five Greek islands in the Aegean Sea.

The camps were built to house 6,200 people.

Moria holds around 19,300 migrants, more than six times its capacity.

Plans to alleviate overcrowding were stalled by the discovery of COVID-19 cases among migrants on the mainland. But Greek officials now plan to move around 2,000 people from the islands, and migration minister Notis Mitarachi said recently that 10,000 had reached the mainland in the first three months of the year.

On Sunday, Mitarachi paid a visit to a medical centre at the Moria camp that is to test asylum-seekers for signs of the coronavirus. Around 150 migrants on the mainland have tested positive for the virus, but up till now, no cases have been reported in the overcrowded island camps.