Four suspected traffickers were arrested Wednesday on suspicion of being linked to the sunken boat, Darmanin told reporters in the French port city of Calais. He said two of the suspects later appeared in court.
The regional prosecutor opened an investigation into aggravated manslaughter after the sinking.
"It's a day of great mourning for France, for Europe, for humanity to see these people die at sea," Darmanin said.
He called for coordination with the UK, saying "the response must also come from Great Britain".
Noting other deadly past incidents involving migrants in the same waters, Darmanin lashed out at "criminal traffickers" driving thousands to risk the crossing.
British Prime Minister Boris Johnson convened a meeting of the government's crisis committee, and Darmanin rushed to see survivors in a Calais hospital. The two governments have long been at odds over how to prevent the crossings, with both sides blaming the other for not doing enough.
Johnson said he was "shocked, appalled and deeply saddened".
A French naval boat spotted several bodies in the water around 2pm and retrieved an unknown number of dead and injured, including some who were unconscious, a maritime authority spokesperson said.
Three French patrol boats were joined by a French helicopter and a British helicopter in searching the area, according to the French maritime agency for the region.
Jean-Marc Puissesseau, head of the ports of Calais and Boulogne, told The Associated Press that he spoke to one of the rescuers who brought some of the bodies to the Calais port.
"Traffickers are assassins," he said. "We were waiting for something like this to happen."
While deaths are occasionally reported on the crossing, such a large number of people losing their lives in one boat is rare.
People fleeing conflict in Afghanistan, Iraq, Eritrea and Sudan have been among those gathered along towns in northern France seeking to cross to Britain.
The number of migrants using small boats to cross the channel has grown sharply this year, despite the high risks that are worsening in autumn weather.
More than 25,700 people have made the dangerous journey in small boats this year — three times the total for the whole of 2020.
With changeable weather, cold seas and heavy maritime traffic, the crossing is dangerous for the inflatables and other small boats that men, women and children squeeze into.
French and British authorities have picked up thousands of migrants off both the French and British coasts in recent weeks in scores of rescue operations.
Darmanin insisted that France has worked hard to prevent deadly crossings, rescuing 7800 people since January and stopping 671 who were trying to cross on Wednesday alone.
"How many more times must we see people lose their life trying to reach safety in the UK because of the woeful lack of safe means to do so?" said Tom Davies, Amnesty International UK's refugee and migrant rights campaign manager.
"We desperately need a new approach to asylum, including genuine Anglo-French efforts to devise safe asylum routes to avoid such tragedies happening again."
Johnson said more needed to be done to "break the business model of the gangsters who are sending people to sea in this way".
Follow AP's global migration coverage at https://apnews.com/hub/migration
