An overnight search was under way in the English Channel into Thursday after four people died following the capsizing of a migrant boat.
The Maritime and Coastguard Agency (MCA) said drones were being used and ships in the area have been asked to post lookouts after more than 30 people were pulled from the freezing water.
A spokesman said on Thursday: “The search has continued overnight utilising a combination of aerial search assets and broadcast action requesting shipping in the area to post lookouts and report any sightings to Dover Coastguard.
“Our thoughts are with those affected by this tragic incident and with the families of those who have lost their lives.”
Prime Minister Rishi Sunak expressed his “sorrow” at the “capsizing of a small boat” in the Channel, telling MPs there had been a “tragic loss of human life”.
A spokesman for a French charity said it was sent a voice message in the early hours of Wednesday from migrants in a waterlogged boat begging for help, and that babies could be heard screaming in the background.
The Royal Navy, French navy, Coastguard and RNLI lifeboats were all involved in the major rescue operation off the Kent coast.
A Government spokesman said authorities were alerted at 3.05am on Wednesday to a “small boat in distress” and there were currently “four confirmed deaths” with investigations ongoing.
“This is a truly tragic incident.
“Our thoughts are with the friends and families of all those who have lost their lives today.”
Government sources initially told the PA news agency 43 people were rescued, but the figure has since been revised to 39 after updated information from authorities involved.
North Thanet MP Sir Roger Gale later told MPs some of the survivors were still in hospital “fighting for their lives”, including women and children.
East Kent Hospitals University NHS Foundation Trust said two causalities were taken to the William Harvey Hospital in Ashford.
It is understood one person was discharged on Wednesday but the other had died by the time they had arrived at the hospital.
Nikolai Posner, communications officer for Utopia 56 which helps migrants in Calais, said the charity received a voicenote at around 2am UK time in which a man said there was water inside the boat and “families and kids” on board.
He told PA: “It was clearly an emergency, he was calling for help … In the background of the message we can hear babies screaming.”
Mr Posner said the charity tried to respond to the message but the reply was not received, then they contacted both the French and UK coastguards.
It is unclear why a rescue boat was only launched an hour after the charity informed authorities of the distress message, Mr Posner said, adding: “We don’t know what really happened during that time.”
Labour leader Sir Keir Starmer said the incident was a reminder that criminal gangs running the crossing routes put “the lives of the desperate at risk and profit from their misery” while shadow home secretary Yvette Cooper warned the action against the gangs has been “too weak”.
There are likely to have been freezing temperatures in the Channel at the time of the tragedy amid a cold snap sweeping across the UK.
It came a day after Mr Sunak unveiled a raft of new measures which he said were aimed at curbing Channel crossings.
More than 44,000 people have made the dangerous crossing this year, Government figures show.
At least 27 migrants died when a dinghy sank while heading to the UK from France in November last year.
Home Secretary Suella Braverman said: “These are the days that we dread.
“Crossing the Channel in unseaworthy vessels is a lethally dangerous endeavour.
“It is for this reason, above all, that we are working so hard to destroy the business model of the people smugglers, evil, organised criminals who treat human beings as cargo.”
Campaigners have blamed the Government’s “hostile” asylum policies for the deaths which they said were “predictable and avoidable”, while Archbishop of Canterbury Justin Welby said the incident showed “debates about asylum seekers are not about statistics, but precious human lives”.
