Malta on Tuesday urged the European Union to launch an "immediate humanitarian mission" in Libya to help stem the flow of illegal migrants during the coronavirus pandemic.

The Mediterranean island nation's foreign minister said the EU teams should distribute food and medical supplies worth at least 100 million euros ($110 million).

Evarist Bartolo's letter to EU foreign policy chief Josep Borrell came a day after border guards reported locating four dingies between Libya and Malta with a reported 258 people on board.

Both Malta and Italy have closed their ports to migrants to curb the spread of COVID-19.

Germany's Sea-Watch International said it feared that one of the boats carrying 85 people had actually capsized and those aboard had drowned.

"Malta denies us safe harbour," the group said on Tuesday. "We demand safe harbour."

The Spanish rescue agency Salvamento Maritimo Humanitario said the migrants it had been in contact with came from sub-Saharan Africa.

The Maltese foreign minister's letter said "the only sustainable and realistic option to avoid this humanitarian crisis... is for the EU to launch an immediate humanitarian mission in Libya".

He estimated there were "over 650,000 people waiting to leave Libyan shores for Europe as the rate of departures accelerates due to conflict, disease and lack of basic needs."

The Maltese foreign ministry argued that delivering aid to Libya -- and not the migrants' sub-Saharan home nations -- was "the quickest way of alleviating and minimising the difficult circumstances that migrants are living in".

Italy has officially attributed 20,465 deaths to COVID-19 -- second only to the United States.

Malta has reported three virus deaths.