British authorities warned that up to 500,000 people could attempt the perilous crossing this summer.

Capt. Nick Cooke-Priest, on the British warship HMS Bulwark, told reporters aboard: “Indications are there that there are 450,000 to 500,000 migrants in Libya who are waiting at the border” for voyage from the North African country’s Mediterranean coast in hopes of reaching Italian shores.

Also aboard the Bulwark, part of a multi-nation patrol and rescue force, was British Defense Secretary Michael Fallon. “We could see hundreds of thousands trying to cross this summer,” Fallon told reporters who asked about the captain’s half-million figure.

During Saturday, a total of 3,480 migrants had been safely rescued in 15 separate operations, the Italian coast guard said. Calls for help went out via satellite phone earlier in the day from the smugglers boats, which included six rubber dinghies and nine fishing boats, all some 45 miles (72 kilometers) off the Libyan shoreline, the coast guard statement said.

Pitching in to save the migrants were Italian coast guard, navy and border police boats and aircraft, a tug boat, two German military ships, the Hessen and the Berlin, and an Irish naval ship LE Eithne.

One Italian navy ship, the Vega, rescued hundreds of migrants from five boats alone on Saturday. Another Italian naval vessel, the Driade, rescued 560 migrants, while the LE Eithne, rescued 310 people, a day after it saved 113 migrants.

Fallon said Europe needed to “pool intelligence, get after the gangs themselves” which are based in Libya and organize the smuggling.

“We can try to cut off their financing. People are making money out of misery, and we can do more there track down the money.”

About 170,000 migrants were rescued at sea last year by Italy. If the British estimates prove true, this year’s arrivals could far outstrip last year’s.

Italian authorities investigating the Libya-based smuggling operations say reliable intelligence is hard to come by, given that Western diplomats have long left Libya, wracked by violence following the 2011 demise of the Moammar Qaddafi regime.

Rival governments command different parts of the country, and tribal and militia clashes aggravate the chaos.

Italy has pressed European partners to do more to help it rescue and shelter masses of migrants fleeing poverty, persecution and conflicts in Africa, the Middle East and Asia.

So far this year, tens of thousands of migrants have arrived in Italy, with many rescued by vessels from Ireland, Malta, Britain and elsewhere. Italy’s coast guard frequently dispatches nearby cargo ships to go to the rescue. Humanitarian organizations also help with rescues at sea, which often occur when smugglers set sail in a dozen or more boats when seas are calm.

Earlier Saturday, police in Sicily detained a suspected migrant smuggler who they said had tried a new tactic of putting only a few passengers aboard a small boat in a bid to land undetected on Italian shores. Ragusa police said a Tunisian man was detained for investigation of smuggling after 12 fellow Tunisians aboard a wooden boat told authorities he promised to sail them to an isolated beach near Trapani, western Sicily, at night so they could slip away undetected. Instead, police say the suspect bungled the route and was spotted by an Italian naval vessel.

Separately, a Gambian skipper suspected of smuggling 116 African migrants was detained by Italian police.