Hundreds of people are feared to have drowned after a boat carrying up to 700 migrants capsized in the Mediterranean Sea, the Italian coastguard says.
A major rescue operation is under way after the vessel carrying “between 500 and 700 migrants” capsized at midnight local time, in Libyan waters south of the Italian island of Lampedusa.
So far 28 people have been rescued.
Since the start of the year, at least 900 other migrants are thought to have died crossing the Mediterranean Sea.
In the past week alone, Italy’s coastguard rescued 10,000 migrants whose vessels ran into trouble.
Italian ships, the Maltese Navy and commercial vessels are all involved in the rescue operation, 130 miles (210km) off the coast of Lampedusa and 17 miles (27km) from the Libyan coast. Twenty-four bodies have been recovered.
The Italian coastguard’s spokesman told the BBC the operation was still focused on search and rescue, “but in time it will be a search [for bodies] only”.
Twenty ships and three helicopters were currently involved in the rescue, he added.
Migrants rescued in past week
Migrants died attempting the crossing between 1 Jan and 15 April 2015
31,500 Migrants have arrived from North Africa so far this year
218,000 Estimated to have crossed the Mediterranean in 2014
3,500 Migrants died attempting the crossing last year
Maltese Prime Minister Joseph Muscat said rescuers were “literally trying to find people alive among the dead floating in the water”.
If confirmed, it would be the biggest migrant tragedy to have taken place in the Mediterranean in recent times, he added in quotes carried by the Times of Malta newspaper.
The migrants reportedly fell overboard when they rushed to draw the attention of a passing merchant vessel, causing their ship to capsize.
At the scene: Richard Bilton, BBC News, Lampedusa
Lampedusa is scrambling to react to the latest horror in the seas off its coastline. Much of the harbour has emptied. Coastguard, customs and fishing boats all left before dawn to help with the rescue.
Marta Bernardini works for the charity Mediterranean Hope, which is based on the island and works with migrants. She told the BBC: “We are very sad. It’s so difficult for us who live and work in Lampedusa every day, to know that a lot of people die in this way, in the Mediterranean Sea.”
Lampedusa is the most southerly point of Italy – nearer Africa than the Italian mainland. Locals say that since January – when the EU took control of patrolling Europe’s maritime borders – between 9,000 and 10,000 migrants have arrived on the island.
There are currently 1,000 migrants in a detention centre on Lampedusa – an island of 5,000 people.
Pope Francis expressed his “deepest sorrow” for the sinking and appealed to the international community to prevent such incidents from happening again.
“These are men and women like us who seek a better life. Hungry, persecuted, injured, exploited, victims of wars. They were looking for happiness,” he said.
It was the Pope’s second appeal in less than 24 hours. On Saturday, he backed a call by Italy for the EU to intervene to stop more lives from being lost.
A maritime rescue operation run by Italy, Mare Nostrum, ended last year after some EU members said they could not afford it and amid concerns it was encouraging more migrants. The EU now runs a more limited border control operation called Triton.
While Mare Nostrum had a monthly budget of €9.5m ($10.3m; £9.6m) and covered much of the Mediterranean, Triton’s budget is less than a third of that at €2.9m ($3.1m), and its remit extends only into Maltese and Italian waters.
Justin Forsyth, chief executive of aid group Save the Children, urged the EU to restart rescue operations.
“The scale of what is happening in the Mediterranean is not an accident, it is a direct result of our policy,” he said.
The European Commission said in a statement that it was working on a new migration strategy which would be adopted in mid-May.
“The only way to truly change the reality is to address the situation at its roots,” it said.
“As long as there is war and hardship in our neighbourhood near and far… as long as countries of origin and transit do not take action to prevent these desperate trips, people will continue to put their lives at risk.”
EU foreign ministers will meet on the migrant issue on Monday.
Last year a record 170,000 people fleeing poverty and conflict in Africa and the Middle East made the perilous crossing to Italy. Thousands died making the journey.