Almost 400 people tried to reach Britain from France over the weekend, the last leg of a migrant trek that for many started in Asia or Africa.
The migrants’ route, which crosses the English Channel as it narrows, also traverses one of the busiest shipping lanes in the world as the smugglers’ dinghies try to avoid massive tankers.
UK authorities said 12 boats carrying 170 people made the attempt on Sunday.
French authorities said another 222 people were stopped from making the perilous journey.
It was not immediately clear if the migrants were stopped at sea or prevented from sailing.
In September, a record 1,951 people completed the crossing but so far in October only 260 have succeeded.
Six migrants in two kayaks tied together were rescued by the French navy near Calais.
There was one report that a body was found on a beach near Calais but it has not yet been confirmed.
A French prosecutor told AFP that the weekend surge in attempts was likely due to improved weather in the Channel.
The government is "taking action at every step of these illegally facilitated journeys to make this route unviable", Home Office minister Chris Philp said.
Migrants have long used northern France as a launching point to reach Britain in lorries through the Channel tunnel or on ferries.
Some have turned to small boats organised by smugglers because coronavirus lockdowns have reduced opportunities to stow away.
