The number of migrants rescued over the weekend while trying to cross the Mediterranean sea surpassed 5,000.

Italian authorities transported 454 to Sicily on Sunday, but 17 others brought ashore in Sicily died, while a European operation to rescue 500 more is still in progress, Reuters reports.

The migrants left war-torn Libya in 25 boats, and were rescued by vessels and aircraft from several European countries including Italy, Britain, Malta, Belgium, Germany, Denmark, Iceland and Finland.

“This is the biggest wave of migrants we have seen in 2015,” Fabrice Leggeri, executive director of the European Union’s border-control agency Frontex, said in a statement. “The new vessels that joined operation Triton this week have already saved hundreds of people.”

Triton, the Mediterranean rescue mission by the E.U. that replaced an Italian initiative called Mare Nostrum, was expanded after it came under criticism after more than 800 migrants drowned in one of the region’s biggest-ever disasters.

The question of how to deal with Europe’s growing refugee crisis, however, still remains a point of contention. Several countries within the E.U. are reluctant to share the responsibility that has primarily been undertaken by the Italian government thus far. Britain opted out of a plan that would have seen refugees sent there from Italy and Greece, while several other countries are reportedly calling for their involvement in rehabilitation efforts to be purely voluntary.

More than 40,000 migrants from Africa and West Asia have been rescued and rehabilitated in 2015 alone, a number that is sure to go up with more boats setting out as the weather gets warmer.

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Write to Rishi Iyengar at rishi.iyengar@timeasia.com.