French authorities say at least 33 migrants have died off the coast of the English Channel. British Prime Minister Boris Johnson said he was “shocked” by the news.

A group of immigrants tried to get from France to Great Britain. But at some point the pontoon they were traveling on flipped over. At the moment, a rescue operation is underway, in which both French and British forces are taking part.

French authorities say at least 33 people have died, but that number could rise dramatically. French Interior Minister Gerald Darmanin He said two people who were traveling on the boat were rescued. This is perhaps the biggest disaster that has ever occurred off the English coast.

French fishermen reported the incident and saw an empty pontoon and dozens of bodies in the water.