Children among dead as boat thought to have been carrying as many as 500 migrants sinks

More than 100 people have died after a boat carrying hundreds of migrants sank off the coast of the Italian island of Lampedusa, with rescuers warning that the number could rise significantly as searches continue for around 250 missing people.

Coastguards said the alarm was first raised early on Thursday morning by fishing boat crews. They reported that a vessel was in trouble near the Mediterranean island that is a frequent destination for people wanting to reach Europe from the north African coast.

The United Nations refugee agency, UNHCR, said it believed there were around 500 passengers, all Eritreans who had boarded in Libya.

On Thursday afternoon Italian rescue divers found some 20 bodies underwater near the boat, a coast guard official said, bringing the total of known dead to more than 100. "The coast guard divers have begun inspections: they have found around 20 bodies around the boat at a depth of about 40 metres," Floriana Segreto told Reuters. She said divers were continuing the search.

The Italian president, Giorgio Napolitano, said the European Union needed to act to stem "a succession of massacres of innocent people".

Initial reports said the boat was believed to have caught fire before sinking. More than 151 people had been rescued, according to the Italian Coast Guard. Lampedusa's mayor, Giusi Nicolini, told news agencies that many more were unaccounted for and children were among the dead.

"It's horrific, like a cemetery, they are still bringing them out," she told reporters.

In a statement, the Italian transport minister, Maurizio Lupi, said 250 people were still missing after what he said was a huge tragedy that was "not humanly tolerable".

"We need to rescue those whose boats sink at sea, a task the men of the coastguard have been seeing to for months, but we also need to do everything possible to stop the traffickers of death who exploit the hope of the poor. It is a duty which we must take on, which the international community and in particular the European Union must take on."

Pope Francis, who visited the island in July on his first papal trip outside Rome, said he felt great pain for the many victims of the shipwreck.

"The word that comes to mind is 'shame'," Francis said in unscripted remarks after a speech in the Vatican. "Let us unite our strengths so that such tragedies never happen again."

Italian media reported that Angelino Alfano, the deputy prime minister and interior minister, would travel to Lampedusa.

Earlier this week 13 men drowned in the waters off Sicily when their boat ran aground. At that time, both Alfano and Lupi, centre-right MPs, were at the centre of an Italian government crisis sparked by Silvio Berlusconi, which absorbed the nation for five days.

Last year, almost 500 people were reported to have died or gone missing while making the crossing from Tunisia to Italy, the UNHCR said. Numbers have been boosted by thousands of refugees from the civil war in Syria.

"I commend the swift action taken by the Italian Coast Guard to save lives. At the same time, I am dismayed at the rising global phenomenon of migrants and people fleeing conflict or persecution and perishing at sea," the UN high commissioner for refugees, Antonio Guterres, said.

Migrants frequently land on Lampedusa, 113km (70 miles) from the coast of Tunisia, often picked up at sea in dangerously overcrowded boats by Italian coastguards.