Four migrants drowned after being swept away by strong currents while trying to cross the Channel.
More than 40 people were rescued off the coast of northern France on Thursday morning.
French authorities said an investigation has been launched after two men and two women died as they tried to climb on to a dinghy at Equihen-Plage, near Boulogne-sur-mer.
Two children were among those taken to hospital as a precaution afterwards and another person was treated for hypothermia.
Government official Francois-Xavier Lauch, the prefect of Pas-de-Calais, told reporters the people who died were “already quite far into the sea”, adding: “The currents, which can be dangerous here, swept them away.”
Other ongoing migrant crossings were being monitored at sea by authorities, Mr Lauch said.
It comes a day after French emergency services took part in a training exercise to practise dealing with migrants in the water at the same beach where the deaths are thought to have taken place, pictures taken by the Press Association show.
Last week two migrants died in a similar crossing attempt – thought to be the first so far this year.
Six others were rescued at Gravelines, near Calais, on April 1, with one person taken to hospital.
Some 17 migrants are confirmed to have died while trying to cross the Channel in 2025, down from 53 in 2024.
More than 5,000 migrants have arrived in the UK after crossing the Channel so far this year, according to Home Office data.
Migrant charities repeated calls for the Government to provide safe and legal ways for asylum seekers to arrive in the UK to prevent more deaths while the Conservatives accused Labour of being “weak” over tackling crossings.
Care4Calais said the tragedies continue as the Government is focused on “ineffective deterrents”, adding: “They could end the deaths on our border overnight by introducing safe routes for refugees to claim asylum in the UK.”
The Refugee Council said policing the Channel alone was “not enough to prevent dangerous crossings” and the UK needed to work with Europe to “share responsibility” over the crisis.
Shadow home secretary Chris Philp accused Labour of being “weak” in its approach.
He said: “Stopping the crossings requires more than disruption on the beaches.
“It requires the swift removal of those who enter illegally so the incentive to make these dangerous journeys disappears.”
Last month the UK and France failed to agree a new beach patrol deal in a bid to cut the number of attempted crossings.
Home Secretary Shabana Mahmood signed a £2 million-a-week extension to the current arrangement as the two governments thrash out a longer-term agreement.
The UK Government said it was “deeply saddened” by the deaths.
A spokesman said: “Every death in the Channel is a tragedy and a stark reminder of the dangers posed by criminal gangs exploiting vulnerable people for profit.
“We will continue working relentlessly with the French and our partners overseas to prevent these perilous journeys.”
