A handful of migrant landings have taken place in recent weeks, including 79 people who arrived last weekend in Italy -- a country under fire even before the outbreak for refusing to allow private vessels carrying migrants to dock.

"If there is no help at sea and countries drag their feet to rescue and allow people to disembark, we're going to end up with a fairly serious humanitarian situation," said Vincent Cochetel, special envoy for the central Mediterranean with the United Nations High Commissioner for Refugees (UNHCR).

At that time, only two rescue boats were in operation -- the Alan Kurdi vessel run by the German NGO Sea-Eye, and Aita Mari chartered by the Spanish organisation Maydayterraneo.

Sophie Beau, general director of SOS Mediterranee, a French-based NGO that charters a rescue boat called the Ocean Viking, questions the motives behind the withdrawal of the two vessels.

Beau warned that "managing the epidemic, closing ports and borders... in addition to these constraints, there is also the lack of a coordinated mechanism," referring to the agreement on the distribution of migrants between European countries after they have disembarked.