Up to 3,400 migrants have been rescued off the coast of Libya, as navies from a number of European countries launched a massive rescue operation in the Mediterranean Sea.

Fifteen rescue operations were carried out in the last 24 hours. Ships from the British, Irish, Italian and German navies have been involved in the operations.

"Migrants are being brought back to southern Italy. About 100 migrants arrived in Lampedusa earlier, and some more are headed to the ports of Palermo and Trapani city in Sicily," Al Jazeera's Hoda Abdel-Hamid, reporting from the Italian island of Lampedusa, said.

"We don't know when the rest will be arriving, because it's simply a logistical nightmare for Italian authorities as many of them are ending up on mainland Italy," she said.

The European navies as part of the Triton Mission rescued migrants from nine wooden fishing boats and six rubber dinghies, our correspondent said.

One million migrants

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

Captain Nick Cooke-Priest, on the British warship HMS Bulwark, told reporters onboard: "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.

There is an uptick in the number of migrants leaving the Libyan coast on weekend. If we compare the number of migrants leaving at this point compared to the last year, there is a radian increase of 30 percent, Al Jazeera's Abdel-Hamid said.

"There are an estimated one million migrants waiting in Libya to cross the sea. These arrivals are an indication that it could be a very busy summer for all the ships that are patrolling the Mediterranean," she said.

Nearly 1,800 migrants are thought to have drowned attempting to make the crossing since the start of this year, including some 800 in one sinking that was the biggest maritime disaster in the Mediterranean since World War II.

That disaster prompted European governments to significantly increase search and rescue operations between Italy and North Africa but they have been unable to agree on a longer-term strategy to ease the migration crisis.

Watch Hamid's previous reports on board the Italian patrol boat: Witnessing rescue efforts for Mediterranean migrants and Rescued migrants reflect on desperate journeys to European waters.