At least 82 people drowned after a boat carrying about 500 African asylum seekers caught fire, capsized and sank near an Italian island on Thursday, officials said.
The Italian news agency Ansa quoted the local mayor of Lampedusa island as saying 82 bodies had been recovered by emergency workers so far, including women and children.
Lampedusa is the island Pope Francis visited in July, one of his first trips outside Rome following his election to the papacy.
"The survivors are in a state of shock. They have been in the water since the early hours of the morning," mayor Giusi Nicolini told news channel SkyTG24, as emergency workers raced to rescue more survivors.
The accident was the latest in many drownings involving migrants travelling on rickety fishing boats or rubber dinghies in the Mediterranean, where thousands have died in recent years.
Nicolini said the migrants had told her they lit a small fire on their boat around half a mile from the shore to attract the attention of coast guards after their vessel suffered engine failure.
The fire then spread, sowing panic on board which caused the boat to flip over and eventually sink. About 150 people were rescued, the mayor said.
Shaken survivors wrapped in thermal blankets — many of them bare-chested — were seen arriving on the dock in images shown on Italian television, as an emergency worker broke down in tears.
The bodies were being taken to an airport hangar because there was no more room in the local morgue on the remote southern Italian island, which has a population of around 6,000.
"This is a tragedy without precedent. In many years of work here I have never seen anything like this," said Pietro Bartolo, a local doctor.
"We don't need ambulances unfortunately, we need hearses," he said.
As hopes faded of finding more survivors, seven boats from the coast guard, border patrol and fire brigade were taking part in the search and were joined by fishing trawlers and pleasure boats.
The navy also said it had deployed one of its patrol ships and was assisting with a helicopter.
The asylum-seekers said they were from Eritrea and Somalia and local police were quoted as saying they believed the boat had left from Libyan shores.
A young Tunisian man believed to be one of the crew members has been detained, Ansa reported.
"The first assistance was provided by people on pleasure boats who heard the screams," Antonino Candela, a local emergency medical worker said.
Candela said Thursday's incident happened shortly after another boat arrived safely in Lampedusa with 463 people on board, believed to be from Syria.
Italian Prime Minister Enrico Letta called the incident "an immense tragedy" in a tweet.
Pope Francis visited Lampedusa in July to plead for more tolerance and attention to the plight of refugees. On Thursday called for prayers.
"This is shameful," the pope said at a Vatican conference. "Let us join forces so these tragedies never happen again. Only decisive cooperation can help to prevent them."
The local archbishop of Agrigento, Francesco Montenegro, said: "We cannot keep on counting the dead. We have to mobilise, do something concrete to avoid these constant tragedies of despair".
Lampedusa is an Italian island lying between Tunisia and Sicily and is a major entryway for asylum-seekers into the European Union, with thousands arriving every year.
"I am dismayed at the rising global phenomenon of migrants and people fleeing conflict or persecution and perishing at sea," UN High Commissioner for Refugees Antonio Guterres said in a statement.
"I commend the swift action taken by the Italian coast guard to save lives," he said.
There has been an increase in the incidents off Italy in recent weeks amid an upsurge in arrivals -- mainly from Egypt, Eritrea, Somalia and Syria.
On Monday, 13 Eritrean asylum-seekers drowned as they tried to swim ashore when their boat ran aground off Sicily near the city of Ragusa.
In a similar incident near Catania in another part of Sicily in August, six young Egyptian men drowned trying to reach the shore.