Criminal networks are making millions of euros a year smuggling migrants across the Mediterranean, with each boatload typically earning €80,000, a top Italian prosecutor said today.

Prosecutors in Palermo on Monday broke up a major people-smuggling ring, just a day after as many as 900 drowned when their boat capsized off the Libyan coast.

Today, Palermo Chief Prosecutor Francesco Lo Voi said this week's probe had helped expose other groups, which are gearing up to handle as many as one million migrants he estimates are in Libya and hoping to cross the sea to Europe.

"During this investigation, we discovered that there are other parallel criminal networks and organisations which work in the same field," Lo Voi told Reuters in his office in the labyrinthine courthouse known for its historic fight against the Sicilian Mafia.

Each criminal group is earning "probably millions of euros" per year and "they are organising themselves to face the increasing requests" to go to Europe, Lo Voi said. Investigations into the smuggling groups are continuing, he said.

In one telephone conversation police recorded during the probe, smugglers said they made an average of €80,000 on each boat, charging migrants as much as €1,500 each for passage.

Dozens of dangerously overcrowded boats are known to have tried to cross from Libya so far this year. Italy estimates as many as 200,000 people will cross to its shores this year, up from about 170,000 reported by the International Organisation for Migration for last year.

A green light to use of military force to fight the smugglers did not appear likely to be agreed at an emergency summit of EU leaders in Brussels today, though the bloc was poised to boost its rescue potential after Sunday's tragedy.

Lo Voi declined to comment on whether military action would help stem the tide of migrants, saying it was a matter for policy makers and not prosecutors.

He did say there was no evidence Islamic terrorists were using the boats to reach Europe.

"We do not have so far any specific evidence allowing us to think that some terrorists could have arrived in Sicily and in Italy" via the migrant boats, Lo Voi said.

Investigators have struggled to track down the cash made by people-smugglers and the boss of the ring targeted this week remains at large in Libya.

The bosses "do not risk their own lives on the sea. They stay behind. They collect the money. They then launder and invest it," Lo Voi said.