A British man attempting to swim the Channel died off the French coast early Sunday, local authorities in northern France said.

The unnamed man in his 40s, who had left from Dover, was only 3.5 kilometres (just over two miles) off France when he was taken ill on board the boat accompanying him, the Pace Arrow, they said.

Regional emergency services were alerted at 2.50 am and sent a helicopter from Le Touquet with a medical team on board as well as a speedboat of rescuers from Calais, but despite several attempts, they were unable to revive the man.

Maritime officials said swimming the Channel was not allowed in French territorial waters because of the dangers posed by the busy shipping lanes and sometimes difficult weather conditions.