Two adults and two children have died after a boat carrying migrants sank, French officials have said.
A large search and rescue operation began earlier after the vessel was seen in difficulty near Dunkirk.
Two children – aged five and eight – and a man and a woman have died. Fifteen others have been taken to hospital, French officials said.
Home Secretary Priti Patel said the “tragic news highlights the dangers that come with crossing the Channel”.
“I will do everything I can to stop callous criminals exploiting vulnerable people,” she said.
The search operation is ongoing off the coast of Dunkirk, according to the Prefecture of the Nord department.
Conditions in the English Channel have been rough throughout the day, with a gale warning issued overnight by the Met Office.
Dover MP Natalie Elphicke said it was “terrible that tragedy has struck in the Channel again”, adding: “People traffickers have no regard for life, no matter how old or young.”
The stricken vessel was first spotted by a passing sailboat at about 09:30 local time, which alerted French authorities.
Four French vessels, one Belgian helicopter and a French fishing boat have been taking part in the rescue operation.
An investigation has been opened by the public prosecutor in Dunkirk to try to identify the cause of the sinking.
More than 7,400 migrants have reached the UK in small boats this year, up from 1,825 in 2019.
The UK government has vowed to make the crossings “unviable” and called for boats to be stopped at sea and returned to France.
The UN Refugee Agency said in August it was “troubled” by the plans to intercept and return boats, adding that the numbers making the crossing “remain low and manageable”.
Charity Care4Calais said the “loss of life should be a wake-up call for those in power in France and the UK”.
It said creating a new system which would allow asylum-seekers to apply for refuge in the UK from outside its borders would “put an end to terrifying, dangerous sea crossings and stop tragedy striking again”.
At least two other people are thought to have died while attempting the crossing this year, with one body found on a beach near Calais on 18 October.
Abdulfatah Hamdallah, from Sudan, died while trying to row to the UK in August.