An Italian coast guard vessel is seen with an helicopter during the search and rescue operation underway after a boat carrying migrants capsized overnight, with up to 900 feared dead, in this still image taken from video April 19, 2015. [Photo/Agencies]

Nevertheless, Chancellor Angela Merkel said that alongside efforts to fight trafficking, more should be done to save those at sea: "We will do everything to prevent further victims from perishing in the most agonising way on our doorstep."

The vessel overturned and sank off the coast of Libya on Sunday, apparently after passengers rushed to one side to attract attention from a passing merchant ship.

A Bangladeshi survivor told police there had been 950 passengers onboard, many locked into the hold and lower deck. However, Catania Chief Prosecutor Giovanni Salvi, who is conducting a homicide investigation into the case, said the figure needed to be treated with caution.

In the Maltese capital of Valletta, coast guard officers brought ashore 24 corpses found so far. Wearing white protective suits, they carried the victims in body bags off the Italian ship Gregoretti and deposited them in hearses as survivors looked on from the deck.

Twenty-seven survivors rescued so far arrived in the Sicilian port of Catania late on Monday. Another survivor was earlier taken to a Catania hospital by helicopter.

In Greece, more than 90 people were rescued from the boat wrecked off the coast of Rhodes: "We have recovered three bodies so far - that of a man, a woman and a child," a coast guard official said.

Among those calling for more compassion from Europe were the United Nations human rights chief and Pope Francis.

"This is a humanitarian emergency that involves us all," the IOM's Italy Director Federico Soda said, calling for a mission equivalent to the Italian operation to be relaunched immediately.