The day after at least 27 people died trying to cross the English Channel when their flimsy inflatable boat capsized during the perilous voyage, the leaders of France and England vowed to crack down on migrant crossings even as they offered a fractious response to one of the deadliest disasters in recent years involving migrants trying to cross the narrow waterway separating the two countries.
French officials confirmed that children and a pregnant woman were among those who had drowned, as crews worked in the cold and wind to recover bodies and to try to identify those who died. Two people, one from Iraq and one from Somalia, were found and taken to a French hospital, where they were being treated for severe hypothermia.
The tragedy was a stark reminder that five years after authorities dismantled a sprawling migrant camp in Calais, both countries are still struggling to handle the flow of migrants in the area.
France and Britain have long accused each other of not doing enough to curb attempts to cross the Channel. After the tragedy on Wednesday, Prime Minister Boris Johnson of Britain said greater efforts should be made to allow joint patrols along the French coast.
And President Emmanuel Macron of France said he expected the British “to cooperate fully and to abstain from using this dramatic situation for political means.”
The two leaders spoke by phone late on Wednesday and said in statements afterward that they had agreed to step up efforts to prevent migrants from making the journey across one of the world’s busiest shipping lanes.
Under an agreement between the two nations, Britain pays France to clamp down on crossings through surveillance and patrols.
Mr. Johnson said that he was “shocked and appalled and deeply saddened by the loss of life at sea in the Channel.” But, he added: “I also want to say that this disaster underscores how dangerous it is to cross the Channel in this way.”
Mr. Macron called for an immediate tightening of border controls and an increased crackdown with other European nations on people smugglers.
“France won’t let the Channel become a graveyard,” he said in a statement.
The drownings came only a few days after French and British authorities had reached an agreement to do more to stem the number of people taking to the sea.
Attempts to reach Britain in small boats have increased in recent years as the authorities have cracked down on the smuggling of asylum seekers inside trucks crossing by ferry or through the Channel Tunnel.
Since the beginning of the year, there have been 47,000 attempts to cross the Channel in small boats and 7,800 migrants had been saved from shipwrecks, according to French officials. Before Wednesday, seven people had died or disappeared so far this year.
Many migrants — who are often from countries in Africa or the Middle East like Iraq and Eritrea — consider Britain an ideal destination because English is spoken, because they already have family or compatriots there, and because it can be relatively easy to find off-the-books work.
But the recent increase in attempts to cross the English Channel by boat reflects a shift in how migrants are traveling, not in how many, according to migration experts and rights groups, who say that, overall, asylum applications in Britain are down this year.
The crossings have become another element in the worsening relations between France and Britain, which have also clashed over fishing rights and trading checks after Britain’s departure from the European Union, as well as over a submarine alliance between Australia, Britain and the United States that undermined a previous French deal.
On a clear day, it is possible to see the white cliffs of Dover from France. The English coast can appear tantalizingly close and for years, it has drawn migrants who have already traversed Europe and hope to reach Britain where they believe better opportunities await.
In the dark of night on Tuesday, nearly three dozen people, including men, women and children, set off on what French officials described as an “extremely fragile” inflatable boat into the strong currents and the freezing, choppy waters that divide the two nations.
It is one of the busiest shipping routes in the world and the short distance belies the dangers inherent in the crossing. The perils are made greater by the fact that many of those attempting the journey are assisted by smugglers who pack them onto tiny dinghies, which are overstuffed and unbalanced.
Gérald Darmanin, France’s interior minister, said that the authorities believed about 30 people were crowded onto a frail vessel that he compared to “a pool you blow up in your garden.”
A report in the French news media said that the migrant boat was struck by a container ship, although French authorities said the circumstances of the disaster were still under investigation.
On Thursday, Mr. Darmanin told RTL radio said that many crossings started in the same way.
“Dozens, sometimes hundreds of migrants, take a beach by storm to leave very quickly, often at high tide, to reach England in makeshift vessels,” he said.
On Wednesday afternoon, a fishing vessel alerted maritime authorities that several people had been spotted in the waters off the coast of Calais. Ships and helicopters soon began a search and rescue operation.
Two people, one from Iraq and one from Somalia, were found and taken to a French hospital, where they were being treated for severe hypothermia. The boat itself was discovered completely deflated, officials said. It was still unclear as of Thursday morning how many people might still be missing.
And the work of identifying those who died was likely to be complicated by the fact that many migrants dispose of any identification papers before making the crossing. Mr. Darmanin said that the dead included women and children. It was still unclear on Thursday where all of the migrants in the group were from.
Mr. Darmanin said that authorities suspected the vessel had been bought in Germany by a smuggler whose car had German license plates. That smuggler, and four others, had been arrested in connection with the shipwreck, Mr. Darmanin said.
Sixty to seventy percent of the migrants attempting to reach Britain arrive from Germany or the Netherlands and go through Belgium into France to attempt a quick crossing, Mr. Darmanin added.
“Smugglers pick them up and, over a couple days, try to bring them to the beach,” he said. “It’s an international problem.”