At least 82 people have died after a boat carrying African migrants sank off the southern Italian island of Lampedusa, the island's mayor says.

More than 140 have been rescued but hundreds are missing, officials say.

Passengers reportedly threw themselves into the sea as the vessel got into trouble and Italian officials were quoted as saying that dozens of people were still in the water.

Earlier this week, 13 migrants drowned while trying to reach Sicily.

In the latest incident, there are reports that a fire broke out on board before the boat sank. It was believed to have been carrying about 500 people.

The boat had set off from Libya and many of those on board were migrants from Eritrea, according to UNHCR spokesman Laurens Jolles in Rome.

Local media reports say that at least one child and a pregnant woman are among the dead.

"The immense tragedy at Lampedusa... is unbearable for any human being," Italian Transport Minister Maurizio Lupi said, according to Reuters.

The mayor of Lampedusa, Giusi Nicolini, described the scene as a "continuous horror".

Pope Francis sent a Twitter message calling for his followers to pray for the "victims of the tragic shipwreck off Lampedusa". In July he visited the island and condemned the "global indifference" to the plight of migrants trying to arrive there.

At this time of year, when the Mediterranean tends to be calmer, vessels carrying migrants from Africa and the Middle East land on Italy's southern shores almost every day, the BBC's Alan Johnston reports from Rome.

But often the vessels are overcrowded and are not seaworthy.

The UN said almost 500 people were reported dead or missing at sea during 2012 in attempts to reach Europe.

On Wednesday a draft report from human rights body the Council of Europe said that Italy was "ill-prepared for a new surge of mixed migration on its coasts".

Italy's system for receiving and processing migrants and asylum seekers was not fit for purpose, a council committee on immigration said.