Nearly 600 people may have drowned when a boat broke up off the coast of Libya, the United Nations refugee agency reported Tuesday as it called on European countries to urgently improve their mechanisms for rescues at sea.

The exact death toll from the latest tragedy remains unknown, but most of the passengers are believed to have been from sub-Saharan Africa, according to Melissa Fleming, a spokesperson for the UN High Commissioner for Refugees (UNHCR).

Passengers say the ship – which broke up shortly after departing Tripoli last Friday – was carrying about 600 people. A diplomat based in the Libyan capital reported that 16 bodies have been recovered so far, including those of two babies.

In the wake of the latest reports of drowning deaths of people fleeing Libya by boat, the UN refugee agency on Tuesday reiterated its call for European nations to urgently improve mechanisms for rescue at sea.

Fleming told journalists in Geneva that UNHCR is urging "States, commercial shipping companies and others present in the Mediterranean to consider that all boats leaving Libya for Europe are likely to require assistance."

She also appealed to ship masters to be extra vigilant and to continue to adhere to the long-standing maritime obligation of aiding people in distress.

UNHCR first appealed to European States early last month to urgently put in place more reliable and effective mechanisms for rescues at sea.

Europe has, until now, received less than two per cent of the people fleeing Libya to escape the continuing conflict in the North African country – but the number of people risking the boat journey is rising.

Fleming added that five boats carrying almost 2,400 people, including many women and children, arrived on the Italian island of Lampedusa on Saturday and Sunday.

"All five boats needed rescuing by the Italian coastguard and maritime police, with one boat running aground close to the Lampedusa shore," she said. "Yesterday three bodies washed ashore, thought to have been passengers from the boat that ran aground."

The number of people who have arrived in Italy and Malta from Libya since the crisis there started in mid-February stands at 12,360. Before Friday's sinking, family members and survivors told UNHCR of boats running into problems, and as many as 800 people are unaccounted for.