At least 12 migrants died off the northern French coast on Tuesday while attempting to cross the Channel to England in the deadliest such disaster this year, the French government said after a major rescue operation.

The boat ran into trouble off Wimereux, a town some five kilometres from France's Boulogne-sur-Mer on the French coast.

According to Frédéric Cuvillier, the mayor of Boulogne-sur-Mer, about 70 people were on board the boat that crashed off the coast of northern France.

Additionally, French Interior Minister Gerald Darmanin announced the death toll on X and said that two migrants were still missing.

A source close to the investigation said the dead included three minors.

According to the Boulogne-sur-Mer prosecutor, Guirec Le Bras, the migrants who died were mostly from Eritrea. Among them, 10 were female and two male, he said. Half the total were minors, AFP reported.

Crew on a French government-operated ship, the Minck, were the first to become aware of the emergency and to respond, naval officer Etienne Baggio said.

French navy helicopters, fishing boats and military vessels were mobilised for the operation, he said, adding that 53 people were rescued.

It was the deadliest such disaster this year which has already seen 25 people die in migrant crossings, up from 12 in 2023.

The French and British governments have for years sought to stop the flow of migrants, who pay smugglers thousands of euros per head for the passage to England from France aboard small boats.

UK interior minister Yvette Cooper called the deaths on Tuesday "horrifying and deeply tragic".

She criticised the "gangs behind this appalling and callous trade in human lives", adding they "do not care about anything but the profits they make".

British Prime Minister Keir Starmer and France's President Emmanuel Macron had earlier this summer pledged to strengthen "cooperation" in handling the surge in undocumented migrant numbers.