After sending distress calls due to a failed engine and an overcrowded boat, a boat full of migrants sank on Wednesday off the coast of Greece, killing at least 79 migrants while hundreds more are believed to be missing, according to reports.

The fishing vessel was traveling from Tobruk, Libya, bound for Italy, full of migrants from mostly Egypt, Pakistan and Syria, who were seeking asylum from violence and political upheaval, reported The New York Times.

What happened?

Alarm Phone, an organization that reaches out to the European Coast Guard and demands aid for those who trigger an emergency alarm by calling, said they received multiple calls of distress. The migrants on the boat said they worried about the number of people on the boat, estimating that 750 people were onboard and covering every square inch of the deck.

The group said the first call came in on Tuesday morning and throughout the day it was eventually able to get the coordinates of the boat, which the group said were passed along to the Hellenic Coast Guard of Greece.

Earlier that same day, Italian authorities had notified Greece about a distress call they received coming from international waters, per a statement by the coast guard. Greek officials said that several offers of assistance were declined by those on board, saying they wished to continue on their journey to Italy.

With many people on board, there’s speculation that there could have been a disagreement about accepting help, reported The Washington Post.

On Wednesday night, the boat sank from what the Greek coast guard described as “a right turn, then a sharp left, and then another right so big that it caused the vessel to capsize,” reported the Times. It sank within 15 minutes.

Greek officials rescued 104 survivors 45 miles off the Greek coastal town of Pylos. They were flown to a hospital in Kalamata, per the Post.

What’s next?

Search and rescue is ongoing but it’s still unclear how many people are missing without a firm number on how many passengers were on board, reported the Times. The wreck sank in 13,000 feet of water, which would put it and its victims out of the range of divers.

Perspective: Refugees dumped at sea