At least 40 people died and 51 others were rescued after a boat carrying mostly sub-Saharan African migrants sank off Libya's coast east of Tripoli, the Libyan government said on Sunday.

The vessel appeared to have got into difficulty around 37 miles (60 km) east of Tripoli, Rami Kaal, a spokesman for the Libyan ministry of interior said.

Libya's porous borders with its sub-Saharan neighbours and its proximity to Italy and Malta across the Mediterranean have made the North African country a common transit route for migrants trying to reach Europe.

With their coast guard, navy and armed forces ill-equipped and still in training, Libyan officials want more help from Western partners to stem the flow of illegal migrants trying to cross through Libya to Europe.

In March, Italy's navy rescued more than 4,000 migrants from overcrowded boats in the Mediterranean sea south of Sicily in just four days.

Many migrants pay more than $1,000 to criminal gangs for the sea journey from Libya, where the government struggles to control a country still full of weapons and brigades of former rebels since the civil war that ousted Muammar Gaddafi in 2011. -Reuters