At least three men died attempting to cross the Channel in small boats on Sunday morning, the French Prefet Maritime for the Channel and the North Sea said.
The UK government blamed their deaths on “ruthless criminals” trying to overload “unseaworthy” boats.
Border security and asylum minister Dame Angela Eagle said: “This morning lives have been lost at sea because ruthless criminals running the small boat trade are overloading people into unseaworthy vessels.
“We continue to support the French authorities who are leading on the response to the incident, which took place in French waters.”
French authorities confirmed the three deaths on Sunday morning following an incident off the coast at Sangatte, near Calais, in which 45 people were rescued after trying to board a small boat bound for the UK.
Local activists said they found at 6am on the beach dozens of people who appeared wet and suffering from hypothermia.
According to reports, tensions rose after around 50 extra migrants of Syrian origin tried to board a small boat that already had 60 people on it and was departing from a beach near Sangatte.
“A group of Sudanese citizens were supposed to leave and Syrians who were not expected wanted to get on board. There was a fight,” Sangatte's mayor Guy Allemand told local daily La Voix du Nord.
The small boat continued its route towards the UK with some migrants returning to the shore. The state has deployed a national navy helicopter, the maritime prefecture said, as it continues to look for survivors.
Light winds have led to more migrants attempting the crossing since Christmas. Between Wednesday and Saturday, nearly 1,500 people arrived in English waters aboard small boats that are often overloaded, according to figures released by the British authorities.
“It doesn’t stop, it’s crossing after crossing, there’s no drop, quite the contrary,” Mr Allemand said. In addition to the three migrants who died, seven people are in a state of “relative emergency” and have been brought to local hospitals, he said.
The deaths, which occurred in French waters, are the first in the Channel since October and bring the total number of people who have died attempting the crossing this year to at least 76.
Since January, more than 36,000 people have successfully made the crossing – up almost 24 per cent on 2023's figure of 29,437, although more than 20 per cent fewer than the record year of 2022, when 45,755 made the journey.
“Many departures” took place again on Sunday morning, according to the maritime prefecture.
UK Prime Minister Keir Starmer has vowed to cut small boat crossings by “smashing the gangs” responsible for them, including through greater co-operation with international law enforcement and establishing a beefed-up border security command in the UK.