At least 12 migrants died on Tuesday after their boat capsized on its way across the Channel to Britain, French Interior Minister Gerald Darmanin said, adding that rescue operations were underway to find two people still missing.
In a sign of the severity of the situation, Darmanin said he would travel to the site, near the town of Boulogne-sur-Mer.
Tackling illegal immigration has been a priority for both the British and French governments. More than 2,000 people have arrived in Britain on small boats over the past seven days, according to UK government figures.
Last week, French President Emmanuel Macron and British Prime Minister Keir Starmer pledged to work closer together to dismantle migrant smuggling routes.
British interior minister Yvette Cooper called the death of the migrants a "horrifying and deeply tragic incident" and said the work to dismantle "dangerous and criminal smuggler gangs and to strengthen border security is ... vital and must proceed apace".
The Channel is one of the world's busiest shipping lanes and currents are strong, making the crossing on small boats dangerous. In August, two people were found dead after a boat carrying migrants trying to cross the Channel ran into difficulties.
"Every political leader, on both sides of our Channel, needs to be asked how many lives will be lost before they end these avoidable tragedies?" Steve Smith, CEO of Care4Calais NGO said.
"Their continued obsession, and investment, in security measures is not reducing crossings, it is simply pushing people to take ever increasing risks to do so."

Shooting at Australia's Bondi Beach kills 12
Police hold person of interest after Brown University shooting leaves two dead
Hamas says Israel's killing of senior commander threatens ceasefire
Ukraine's Zelenskyy ditches NATO ambition ahead of peace talks
Thailand declares curfew along coast as Cambodia border fighting spreads
India tightens pollution curbs as Delhi's air quality worsens
'Peace is not far away' says Erdogan after Putin meeting
Belarus frees Nobel winner, protest figures as US lifts more sanctions
