Government has said, a migrant boat that was having trouble crossing the English Channel in the early morning hours lost at least three passengers.
43 people had reportedly been saved, with more than 30 of them being pulled from the water, according to a source close to the situation, BBC’s Nick Eardley reported.
In frigid waters between Kent and France, a sizable search and rescue operation was started.
The home secretary expressed her “heartfelt thoughts” to all parties involved.
The BBC’s political correspondent Nick Eardley said the number of deaths could rise further.
The boat is likely to have been carrying migrants risking the crossing from France, a day after Prime Minister Rishi Sunak announced new measures to “stop the boats”.
It is understood the small boat got into trouble at about 03:00 GMT off the coast of Dungeness, 30 miles west of Dover.
The UK coastguard, the French Navy and an air ambulance were all sent to help with the rescue operation.
A fishing boat in the area and coastguard helicopters from Lydd and Lee on Solent were also involved.
South East Coast Ambulance Service said it was called following reports of the incident, and sent crews to Dover, in Kent, to help with the follow-up operation.
Overnight on Tuesday, temperatures dropped to 1C, with it likely to have been colder out at sea. A yellow weather warning for ice was in place across Kent at the time.
Dover MP Natalie Elphicke said she was “very saddened” to hear of the tragedy, and her thoughts and prayers were with all of those involved.
This latest search and rescue follows a fatal incident in November 2021, when at least 27 migrants died after a dinghy sank while heading to the UK from France.
The BBC’s Simon Jones said 460 people made the journey from France to Kent in small boats between Friday and Sunday.
Nearly 45,000 people have made journey this year so far.