At least nine migrants died and 48 are missing after their boat capsized early on Saturday near the Spanish island of El Hierro, rescue services said, in what threatens to be the deadliest such incident in 30 years of such crossings to the Canary Islands.

The emergency services were able to rescue 27 of 84 migrants who were trying to reach the Spanish coast, they added. Spanish authorities said the migrants were from Mali, Mauritania and Senegal.

The rescue team received a call shortly after midnight local time from the boat, which was located around four miles east of El Hierro. It sank during the rescue, they said.

“All the migrants on board concentrated in the same side of the boat during the rescue, which made it capsize. Everyone fell into the sea,” said Manuel Barroso, head of Spain’s maritime rescue services.

Wind and poor visibility made the rescue extremely difficult, he added.