Six people have died after a boat carrying migrants sank in the Channel.
A spokeswoman from French coastal authority Premar said between five and 10 others are missing, AFP reports.
British and French coastguards have rescued around 50 people from the vessel, authorities said.
A number of people were seen being brought off a lifeboat, some on stretchers, in Dover, but the extent of injuries and exact numbers remain unclear.
Ten people were taken to Dover and the others to Calais.
A passing ship first raised the alarm that an overloaded boat was in difficulty off the coast of Sangatte, near Calais in the early hours of Saturday, French authorities said.
When the French lifeboat arrived, they found numerous people in the sea, with some screaming for help. The Dover lifeboat, which was already in the Channel dealing with another boat carrying migrants, joined the rescue operation.
Rescuers are still scouring the water for survivors and bodies - often boats are so overloaded it is difficult to tell how many people are on them. A French Navy aircraft and a helicopter have been deployed to help the search.
The MP for Calais, Pierre-Henri Dumont, said authorities are interviewing the migrants who are able to speak and not too unwell, to establish what happened and where they are from.
Rescue crews say this is the seventh time this week that they have had to pull people from the water.
Although the incident happened in French territory, with these types of operations, British and French rescue teams work together to rescue as many people as possible.
A volunteer, who was on one of the rescue boats, told Reuters news agency migrants were using shoes to bail water out of the sinking boat.
Anne Thorel said there had been "too many" people on board.
A French prosecutor told the AFP news agency that the first of the victims was an Afghan man aged between 25 and 30.
Enver Solomon, chief executive of the Refugee Council, thanked the rescuers for their efforts but urged the UK government to work on creating an "orderly and humane asylum system".
The English Channel is one of the most dangerous and busiest shipping lanes in the world, with 600 tankers and 200 ferries passing through it every day.
The UK Home Office has been asked for more details about the incident. Home Secretary SuellaBraverman called what happened a "tragic loss of life".
Dover MP, Natalie Elphicke, said the incident highlighted the need for joint patrols on the French coast.
"These overcrowded and unseaworthy death traps should obviously be stopped by the French authorities from leaving the French coast in the first place," she said.
On X, formerly known as Twitter, shadow immigration minister Stephen Kinnock said it was an "appalling, deeply shocking tragedy".
Another small boat also got into difficulty but all on board have been rescued, the UK Coastguard said.
In the last two days more than 1,000 people made the journey across the Channel, government figures show.
The incident comes after the UK government faces pressure over fears of a Legionella outbreak on its new migrant barge, Bibby Stockholm. The first migrants to board the vessel had to be removed after bacteria was found in the water system.
