One person has died after a small boat carrying more than 60 capsized in the English Channel while attempting to reach the UK, French authorities said on Friday.
Another person is in a critical condition and is receiving treatment in Calais.
There were 66 people on the boat when it capsized about 8km off the coast of northern France.
Two more people are "potentially missing", authorities said.
"One unconscious victim, in critical condition, was taken by helicopter to the hospital in Calais, while the second unconscious victim could not be revived," authorities said.
French sea rescue teams at Griz Nez near Calais were informed during the night that an inflatable boat carrying migrants was in difficulty off the coast.
A rescue vessel arrived in the area within 30 minutes at about 12.30am and found the boat deflating and people in the water, authorities said.
Rescuers took everyone they could find back to Calais.
The person they found in a life-threatening condition was taken to hospital by helicopter.
Boats and aircraft are still looking for survivors, with French Interior Minister Gerald Darmanin expected to arrive in Calais on Friday morning.
The UK Coastguard said it had sent a helicopter to assist French authorities.
Two decades after the closure of a Red Cross centre in Sangatte, hundreds of people still live in tents and makeshift shelters near Calais and Dunkirk, hoping for an opportunity to make the crossing hidden in a truck or aboard a small boat.
Tens of thousands of people a year have been attempting the dangerous Channel crossing, making the issue a political priority for the UK and a bone of contention between the governments in London and Paris.
The human toll has been high – one of the worst sinkings two years ago claimed 27 lives.
More recently, in late November, a migrant boat carrying 60 people sank and a man and woman drowned.
In August, six Afghans drowned after their small boat capsized.
100,000 migrants cross the Channel in five years - in pictures
French authorities say that boats setting off are increasingly overloaded, with the average number – about 53 passengers – nearly double that of two years ago.
More than 28,000 people have crossed the Channel this year, according to British government statistics running to the end of November, compared with about 46,000 for all of last year.
British Prime Minister Rishi Sunak made "stopping the boats" to prevent migrants from entering the UK illegally one of his five priorities this year.
This week, he overcame dissent from the right wing of his party as MPs approved a new bill to authorise deportations of asylum seekers to Rwanda after rebels abstained from the vote.
Under the plan migrants who arrive illegally will be removed to the Central African country or sent back to their own country if it is deemed safe.
Mr Sunak said he would work to convert the emergency legislation into law “so that we can get flights going to Rwanda and stop the boats” after winning the crunch vote.
Government minister Andrew Griffith said the confirmation of another migrant death in the Channel showed why the crossing was "not a safe route".
Asked for his reaction on Sky News on Friday, Mr Griffith said: "We are just hearing it now, but all of these are tragic stories.
"It shows once again the importance of cracking down on the terrible trade of people traffickers in the Channel. It is not a safe route, it is not a safe crossing. People shouldn't need to do that.
"It is why it is really important that the government is taking action through things like the Illegal Migration Bill, through the proposals around Rwanda that we debated in parliament earlier this year, to absolutely remove the incentive, break the economic model of people smugglers, so that we can stop this terrible trade."
Enver Solomon, chief executive officer of the Refugee Council, said the latest incident is "yet another terrible and avoidable tragedy".
"These appalling deaths are becoming too common and there is an urgent need to put in place safe routes so people don't have to take dangerous journeys across the world's busiest shipping lane," he said.
"Instead, the government is pushing ahead with its unworkable and unprincipled Rwanda plan as well as shutting down existing safe ways to get to the UK.
"People flee persecution and violence out of desperation, to find safety and protect their families. The government must take action now and respond in a compassionate way to prevent future tragedies and protect human life."
