At least 24 people were killed Monday after a boat suspected of carrying illegal migrants sank north of the Bosphorus Strait off the coast of Istanbul, Turkish authorities reportedly said. Seven people were reportedly rescued while a search-and-rescue operation is reportedly underway.

The boat, which is feared to have sunk from overloading, was carrying at least 40 people from Afghanistan and Syria, The Los Angeles Times reported. Among the dead were several children, the Hurriyet Daily News, a local news source reported. Turkey’s coast guard, local fishermen, a team of divers and a helicopter were reportedly assisting the ongoing rescue operation. The coast guard was alerted after the boat sank about three miles north of the Bosphorus Strait in the Black Sea, media reports said, citing the Istanbul governor’s office.

“The wind is making our task very difficult. The boat is a very small one, it’s in fact just a small boat. But they were carrying 40 people in it. We are seeing bodies of children floating in the sea,” Ali Saruhan, one of the rescuers in the area, reportedly said.

The boat may have hit a vessel “as it sank in a place where there is a lot of traffic,” the Hurriyet reported, citing a fisherman. The local news source also reported that the migrants were heading to Romania.

The Bosphorus Strait, which forms part of the boundary between Europe and Asia, is one of the world’s busiest waterways. In September, the Turkish coast guard rescued a boat carrying nearly 82 migrants reportedly headed to Romania, Hurriyet reported.

Authorities have reportedly launched an investigation into the incident, while two prosecutors were sent to the scene for inspection.