At least 30 people have died and others are feared missing after a boat headed for the UK capsized in the English Channel.
Prime Minister Boris Johnson said he was “shocked, appalled and deeply saddened” about the “disaster” and hit out at people trafficking gangs who are “literally getting away with murder”.
French prime minister Jean Castex called it a “tragedy” and said his thoughts were with “victims of criminal smugglers who exploit their distress and injury”.
Jean-Marc Puissesseau, president and chairman of the ports of Calais and Boulogne, told BBC News: “What I know is that there were 50 people on this boat.
“What I have heard is that there are 30 people who have died, and about five or six who have been found.”
A rescue operation is under way in the Channel by air and sea as French and British authorities search for anyone still in the water.
The emergency search was sparked when a fishing boat sounded the alarm earlier on Wednesday after spotting several people at sea off the coast of France.
Speaking to reporters, Mr Johnson said: “My thoughts and sympathies are first of all with the victims and their families. It’s an appalling thing that they have suffered.
“But I also want to say that this disaster underscores how dangerous it is to cross the Channel in this way.”
Mr Johnson admitted efforts so far to stem the flow of migrants crossing the Channel in small boats “haven’t been enough”.
He said: “What this shows is that the gangs who are sending people to sea in these dangerous crafts will literally stop at nothing.”
He added: “…there is no doubt at all that the gangs concerned, unless they are shown that their business model won’t work, that they can’t simply get people over the Channel from France to the UK, they will continue to deceive people, to put people’s lives at risk and, as I say, to get away with murder.”
Shadow home secretary Nick Thomas-Symonds said Wednesday’s loss of life must be the “most tragic of wake-up calls” to put a stop to crossings.
He told the BBC: “It is unrealistic to think that the entirety of that coastline can be patrolled.
“We need to be looking at practical law enforcement action away from the coast as well.
“In addition to that we do need to look at safe and legal routes.”
A number of people are also believed to have reached Britain in small boats on Wednesday, with people seen being brought ashore in Dover by immigration officials.
The Dover Strait is the busiest shipping lane in the world and has claimed many lives of people trying to cross to Britain in inflatable dinghies.
More than 25,700 people have made the dangerous journey to the UK in small boats this year – three times the total for the whole of 2020, according to data compiled by the PA news agency.