Rescuers saved 366 migrants from rickety boats trying to cross the Mediterranean to Italy but at least 20 people were reported to have drowned, Italian police said on Saturday.

The survivors, who were rescued in four separate operations, were crammed onto three rubber dinghies and a wooden fishing boat. They were all taken to the Sicilian port of Augusta, where they were questioned on Friday evening by the Italian police unit Interforce, which combats illegal immigration.

The Norwegian ship Siem Pilot went to the aid of one dinghy that sank in the Sicilian Channel, but many migrants were already in the sea when it arrived, Antonio Panzanaro, an Interforce official, told Reuters. One corpse was recovered but survivors said that at least 20 people had drowned before the ship arrived, he said.

There were 82 women and 25 children among the 366 people rescued, he said. The survivors were mainly from Nigeria, Ethiopia, Eritrea and Bangladesh.

Seven people were arrested from the four boats, including their drivers, on suspicion of people-trafficking, he said.

Italy has long been on the front line of seaborne migration from Africa to Europe, and is now the main point of entry after the European Union struck a deal with Turkey to stem flows to Greece amid Europe's worst migration crisis since World War Two.

Slightly fewer migrants arrived on Italian shores in the first six months of 2016 compared with the same period last year, but the number of deaths on the route has risen, according to the International Organisation for Migration (IOM).

More than 67,000 seaborne migrants arrived in Italy between January 1 and July 3, according to the IOM.-Reuters