At least one person died and more than 50 were rescued after a migrant boat trying to cross the Channel from France capsized early on Saturday, local authorities said.

Local mayor Franck Dhersin said a vast rescue operation was launched around 6 a.m. (0400 GMT) as dozens of migrant boats tried to make the crossing at the same time.

"Several of the boats were facing serious difficulties," he told Reuters. "Near (the coastal town of) Sangatte they unfortunately found dead bodies."

The maritime prefecture confirmed that there had been at least one death and said search and rescue operations were ongoing.

The Channel between France and Britain is one of the world's busiest shipping lanes and currents are strong, making the crossing on small boats dangerous.

Human traffickers typically overload rickety dinghies, leaving them barely afloat and at risk of being lashed by the waves as they try to reach British shores.

"We saved 54 people, including one woman," said Anne Thorel, a volunteer who was on one of the rescue boats, describing the migrants' frantic efforts to bale water out of their sinking vessel using their shoes.

"There were too many of them on the (migrant) boat," she told Reuters by phone as she returned to the shore.

Thorel said no one was killed on the boat she was involved with rescuing.

Britain's coastguard said it had sent a lifeboat from Dover to assist with the rescue, along with a coastguard rescue team and ambulance staff.

UK government figures show that the number of migrant Channel crossings since the start of 2018 exceeded 100,000 this week. The number so far this year stands at nearly 16,000.

Prime Minister Rishi Sunak's government has spent the week making announcements about its efforts to reduce the number of asylum seekers, hoping to win support from voters as the ruling Conservative Party trails in opinion polls.