Over two dozen migrants have died while attempting to cross the English Channel from France into Britain.
It's the worst disaster on record involving migrants crossing the Channel, a persistent source of tension between the two countries.
Local fishermen say more migrants than usual left the French shores on Wednesday to take advantage of calmer sea conditions.
France's interior minister Gerald Darmanin said Wednesday that the migrants' boat later deflated.
Officials on both sides have traded blame for the incident.
British Prime Minister Boris Johnson called on France to do more to stem the flow of migrants.
"I say to our partners across the Channel, now is the time for us all to step up, to work together, to do everything we can to break these gangs who are literally getting away with murder."
Meanwhile, French President Emmanuel Macron has accused Britain of politicising the issue for domestic gain.
Regaining control of Britain's borders was a key campaign point for supporters of Britain's exit from the European Union.
In a statement, Johnson said he and Macron agreed to step up efforts to prevent future crossings.
French police have arrested four human traffickers in connection with the incident.
The migrants' nationalities and identities have not yet been reported.