More than 4,000 migrants have been rescued off Libya's coast in 22 separate operations in one day, with rescuers finding 17 people dead aboard a rubber dinghy, the Italian Coast Guard said Saturday.

The rescues, from 13 wooden fishing boats and nine motorized rubber dinghies, took place Friday. In all, 4,243 rescued migrants were being brought to southern Italian harbors, including in Sicily.

Smugglers are reaping millions by overcrowding unseaworthy boats with migrants on Libya's Mediterranean coast to set out for Italian shores. The migrants are fleeing war, persecution or poverty in Africa, the Mideast and elsewhere.

Cargo ships and Irish and German navy vessels helped Italian military craft in Friday's rescues. Italy has demanded its European partners help more with the migrants, who have been coming in huge numbers this year. Last year, Italy rescued some 170,000 migrants at sea.

The latest arrivals, following several days without rescues, followed a pattern. When seas are rough or weather stormy, few or no boats set out. When a spell of calm seas arrives, smugglers launch as many boats as they can, cramming more migrants into the boats than can safely be carried. Many vessels soon run into difficulties. The Italian Coast Guard coordinates rescues after receiving distress calls via satellite phones from the migrant boats, or when the craft are spotted by military patrol boats or aircraft.

Interior Minister Angelino Alfano warned on Saturday migrant arrivals would continue without letup as long as Libya, where rival governments and violent militias hold sway, is plagued by chaos.

The high cost of rescuing and sheltering migrants while they seek asylum is campaign fodder in Sunday's local and regional elections in Italy. Anti-immigrant Northern League leader Matteo Salvini urged voters to choose his party, saying that whoever doesn't "is an accomplice of the invasion" of migrants.