Two children, aged five and eight, are among four people who have died after a migrant boat sank off the coast of France.
The deaths of the children as well as a man and a woman were confirmed by the regional administration for the Nord region.
Fifteen migrants have been saved so far, according to the administration, which stressed the death roll may climb as search and rescue efforts continue.
Sky News understands the boat got into difficulty in rough weather and strong winds when it was in French waters about 2km from the French coast on Tuesday morning.
Around 19 or 20 people were on board the boat in an attempt to get to the UK.
French authorities mobilised five vessels and a Belgian helicopter nearby to help with the rescue after the migrant boat was reported in distress off the coast of Dunkirk, according to the regional French maritime agency.
Those officials had earlier said 18 people were rescued and were receiving treatment in hospitals in Calais and Dunkirk.
The public prosecutor of Dunkirk confirmed it is investigating the cause of the sinking, which is believed to have caused the highest death toll from a single crossing in the current migrant crisis.
In a statement, Home Secretary Priti Patel said she is "truly saddened to learn of the tragic loss of life in French waters this morning" and that her thoughts and prayers are with the victim's loved ones.
"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," she said.
"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."
Such crossings have become more common recently, but confirmed deaths are rare.
More than 7,000 migrants have made it across the English Channel to the UK - up from 1,800 the previous year.
Government figures show four people have died making the journey in 2019 and four so far this year, including a body found on a beach near Calais on 18 October.
In August, Sudanese man Abdulfatah Hamdallah reportedly died while trying to row to the UK.
Ms Patel has called for boats to be intercepted at sea and turned back towards France in an approach that would make the crossings "unviable".
But the United Nations' Refugee Agency expressed concern about the method.
Care4Calais founder Clare Moseley said the refugee community in Calais is "utterly devastated" following Tuesday's deaths.
She said: "We are grieving for the victims, we stand in sympathy and solidarity with their families and friends.
"It is cruel and horrifying that this time, young children are among the victims.
"This unnecessary loss of life has to stop. No one should ever feel they have to get into a fragile craft and risk their lives crossing the Channel, least of all vulnerable children."
