UPDATED 6.45PM: EU foreign affairs chief Federica Mogherini has unveiled plans tackle a growing migrant crisis after telling member states they had "no more excuses" not to act as fresh distress calls rang out in the Mediterranean.

A day after a fishing vessel crammed with migrants capsized off Libya with the loss of hundreds of lives, EU foreign and interior ministers met in Luxembourg on Monday to discuss ways to stem the flood of people trying to reach Europe.

More than 700 migrants are feared dead in Sunday's disaster, with some survivors suggesting nearly 1000 people could have been on board.

As the search for victims continued, the International Organisation for Migration said it had received a distress call from another boat - but cautioned against concluding this was another disaster in the making.

Italian Premier Matteo Renzi said separately that Italy's coast guard had asked merchant shipping to help two boats off the Libyan coast with up to 450 migrants on board after they sought help.

Police in Greece meanwhile reported three people killed, including a child, after a boat coming from Turkey sank off the island of Rhodes.

Dramatic YouTube footage showed people trying to reach survivors huddled on a piece of wreckage as they were being swept towards rocks.

Ninety-three people were rescued alive, police said.

Europe's southern shores have been swamped over the past two weeks with migrants fleeing war and hardship, mostly via conflict-wracked Libya.

Unveiling a 10-point action plan, Mogherini said the 28-member bloc needed "to show that same collective European sense of urgency we have consistently shown in reacting in times of crisis."

The EU had to live up to its humanitarian values and commitments towards migrants, she said, adding: "To send them back is another way of killing them."

First on the list, ministers agreed the current EU border surveillance mission Triton should be increased to extend its range and capabilities on the bloc's southern flank.

Triton replaced Italy's own Mare Nostrum mission which Rome scrapped late last year in protest that its EU partners would not share the burden.

The EU will also try to capture or destroy people smuggler boats and increase cooperation across the board, the European Commission said.

The bloc will offer too a "voluntary pilot project on resettlement, providing a number of places to persons in need of protection," a key but small step forward in spreading the problem.

Up to now, countries relatively untouched by the problem had objected to this form of burden sharing, however small.

Diplomats said there could be 5000 places available but the Commission gave no figure.

EU president Donald Tusk announced an emergency leaders summit for Thursday to discuss the plan, saying: "We cannot continue like this, we can't accept that hundreds of people die."