A boat carrying migrants ripped apart in the English Channel as they attempted to reach Britain from northern France on Tuesday, plunging dozens into the treacherous waterway and leaving 12 dead, authorities said.

Many didn’t have life preservers in what one official called the deadliest migrant accident in the channel this year.

“Unfortunately, the bottom of the boat ripped open,” said Olivier Barbarin, mayor of Le Portel near the fishing port of Boulogne-sur-Mer, where a first aid post was set up to treat victims. “If people don’t know how to swim in the agitated waters … it can go very quickly.”

The mayor said 12 died after initially giving a toll of 13. Lt. Etienne Baggio, a spokesman for the French maritime prefecture that oversees that stretch of sea, said rescuers pulled a total of 65 people from the waters in a search operation that lasted more than four hours. Doctors confirmed 12 did not survive, he said.

Baggio called it the deadliest migrant boat tragedy in the English Channel this year. Many of those aboard didn’t have life vests, he said. It was not immediately clear how the boat ripped open or what kind of boat it was. Some attempt the crossing in rubber dinghies.

The maritime prefecture said the boat got into difficulty off Gris-Nez point between Boulogne-sur-Mer and the port of Calais further north. Sea temperatures off northern France were around 20 degrees C, or about 68 F.

Interior Minister Gerald Darmanin said he was heading to the scene of what he described as the “terrible shipwreck.” Last week, the leaders of France and Britain agreed to deepen cooperation on illegal migration in the channel.

Europe’s increasingly strict asylum rule s, growing xenophobia and hostile treatment of migrants have been pushing them north.

At least 30 migrants have died or gone missing while trying to cross to the U.K. this year, according to the International Organization for Migration. That figure doesn’t include the latest deaths.

At least 2,109 migrants have tried to cross the English Channel on small boats in the past seven days, according to U.K. Home Office data updated Tuesday. The data includes people found in the channel or on arrival.

(AP)