At least 31 migrants have drowned trying to cross the Channel, a French transport official has said.
Calais MP Pierre Henri Dumont earlier told Sky News it was 29, but the reported death toll has been rising over the last few hours.
Other people are thought to be injured after the inflatable dinghy capsized near Calais this afternoon.
One UK patrol boat, one French lifeboat, and three helicopters are involved in search and rescue efforts, said French maritime minister Annick Girardin.
Prime Minister Boris Johnson is holding a meeting of the UK’s emergency COBRA committee in response.
He said he was "shocked, appalled and deeply saddened" by the deaths.
It is the worst-ever incident involving migrants in the Channel, according to French maritime authorities.
Franck Dhersin, deputy head of regional transport, said the number of dead had increased to 31 and that two people were still missing.
France’s interior minister, Gerald Darmanin, is heading to the area and prime minister Jean Castex called it a "tragedy".
Fisherman Nicolas Margolle said he had seen two small dinghies, one with people onboard and another empty.
He said another fisherman had called rescuers after seeing the empty dinghy and 15 people motionless in the water.
A French naval boat retrieved an unidentified number of dead and injured, including some who were unconscious, a maritime authority spokesperson said.
Conditions on the Channel were described as cool but calm, which may explain why there were a number of crossings on Wednesday.
Other migrants were brought ashore at Dover and Dungeness.
The Dover Strait is the world’s busiest shipping lane and more than 25,700 people have made the dangerous journey to the UK this year.
That figure is three times the total for 2020, according to data compiled by the PA news agency.
Dover MP Natalie Elphicke said: "This is an absolute tragedy. It underlines why saving lives at sea starts by stopping the boats entering the water in the first place.
"As winter is approaching the seas will get rougher, the water colder, the risk of even more lives tragically being lost greater.
"That’s why stopping these dangerous crossings is the humanitarian and right thing to do."
© Sky News 2021