A fishing boat crowded with migrants overturned Wednesday in the Mediterranean off Libya as rescuers approached, and the Italian coast guard and Irish navy said at least 367 people were saved, although 25 bodies also were found in the latest human smuggling tragedy.

Coast guard Cmdr. Filippo Marini said the rescue operation, involving seven ships, was still underway several hours after the capsizing. Survivors indicated that between 400 and 600 people were aboard the smugglers' boat, he added.

The exact number of those aboard might never be known, but authorities hoped to have a better idea after survivors are interviewed.

The Irish naval vessel Le Niamh was one of the ships tasked by the coast guard to speed to the rescue of the boat shortly before noon, Irish Capt. Donal Gallagher told The Associated Press by phone.

The Le Niamh arrived near the fishing boat, Marini said, and "at the sight of it, the migrants shifted" to one side and their boat capsized.

An Irish Defense Forces statement said that when it reached the scene, the Le Niamh deployed two rigid hull inflatable boats on either side of the vessel "as per standard procedure. However, the vessel capsized." The Le Niamh deployed life rafts and other rigid hulled boats, it added.

An Italian military helicopter dropped additional life rafts into the sea, where 150 people were initially spotted, Gallagher said.

By evening, the Le Niamh had 367 people aboard, including 13 children, the Irish military said.

Since the water was warm, rescuers worked with hope of finding more survivors, even as dusk approached. The vessel was reported to be 110 kilometers (about 75 miles) northwest of Tripoli, Libya's capital.

In April, a crammed fishing boat sank, taking down with it perhaps as many as 800 migrants trapped inside the hold. Only 28 people, including two alleged smugglers, survived.

Prosecutors in Sicily said smugglers routinely pack unseaworthy boats far past capacity, with hundreds of migrants below deck. Italian navy divers determined that hundreds of migrants were trapped inside the boat when it sank. That boat overturned when a container ship went to its rescue, the smugglers botched the steering, and migrants also rushed to one side, investigators determined.

If it is determined that hundreds were crammed in the hold of the iron fishing boat that overturned Wednesday, there is a real risk that many of the migrants died trapped inside, said Flavio Di Giacomo of the International Organization for Migration, a human rights group.

Di Giacomo said the estimate of 600 aboard was credible because the boat was 20-25 meters (70-85 feet) long, and smugglers, who don't like to leave any space unused, usually fit about 600 aboard a fishing boat of that size.

Also involved in Wednesday's rescue were an Italian vessel and a boat operated by Doctors Without Borders.

Non-governmental organizations or cargo ships in the vicinity frequently help rescue migrants, with operations coordinated by Italy's coast guard and under the umbrella of a European Union task force known as Triton.

On Tuesday, the International Organization for Migration said nearly 2,000 migrants are believed to have died at sea since the start of this year, but the exact toll isn't known.

Fleeing war, persecution and poverty, the migrants travel overland for weeks or months from sub-Saharan Africa, the Horn of Africa, the Middle East and parts of Asia to reach Libya. Once there, they set sail in flimsy motorized rubber dinghies or rickety fishing boats. When the vessels have problems, often someone aboard contacts the coast guard by satellite phone to request rescue. Other boats in distress are spotted by Triton air surveillance.

Most of the migrants hope to find asylum, relatives or jobs, mainly in northern Europe.