The deaths of two young children and two adults as they attempted to reach the UK in a migrant boat should be a “wake-up call” for politicians on both sides of the Channel, charity bosses have said.
Another 15 migrants were rescued, with eight suffering hypothermia and two in cardiac arrest, local firefighters said.
French authorities have said further searches are being carried out in the area and the death toll could rise.
The tragedy is believed to be the single biggest loss of life during the current migrant crisis, bringing the total number of deaths since 2018 to 10.
Clare Moseley, founder of refugee charity Care4Calais, said the “horrifying” incident should be a “wake-up call” for leaders in the UK and France.
“We are grieving for the victims, we stand in sympathy and solidarity with their families and friends,” she said.
“It is cruel and horrifying that, this time, young children are among the victims.”
She added: “We have to provide a safe and legal process by which refugees can have their UK asylum claims heard, that’s the way to put an end to terrifying, dangerous sea crossings and stop tragedy striking again.”
Charity Save the Children has called for London and Paris to “come up with a joint plan that ensures the safety of vulnerable children and families”.
“The English Channel must not become a graveyard for children,” it warned.
Ms Patel added: “We are in touch with our French counterparts who are leading on the response and have offered whatever support they need as they investigate this incident.
“This tragic news highlights the dangers that come with crossing the Channel and I will do everything I can to stop callous criminals exploiting vulnerable people.”
French citizenship minister Marlene Schiappa said she felt “great sadness” in light of the incident.
“Despite the resources of the state, which were all mobilised in the SOS operation, the losses are heavy and the final toll is still uncertain,” she said.
The people on board the migrant boat had been trying to reach the UK despite wind gusts of up to 18mph.
After the vessel was seen in difficulty, French patrol boats and a helicopter were dispatched, as well as civilian boats.
Fifteen people were taken to hospitals in Calais and Dunkirk, according to the Maritime Prefecture of the Channel and the North Sea.
An investigation is under way into the cause of the sinking.