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.
Seven migrants are now confirmed to have died crossing the English Channel illegally since the start of 2020, according to figures provided by the authorities – compared to a total of four in 2019.
In recent years, attempts to cross the busy 30-kilometre shipping lane have been increasing, according to the French maritime prefecture of the Channel and the North Sea.
Labour MP Yvette Cooper, chair of the home affairs select committee, said it was “truly awful”, adding that criminals were profiting from “other people’s desperation”.
The committee is looking at the rise in Channel crossings and “the work that is urgently needed to prevent more lives being lost”, she said.
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. A total of 2,358 people were rescued and brought back to French or British coasts in 2019, compared with 586 in 2018.