The UK coastguard is co-ordinating a search-and-rescue operation after several boats of migrants crossing from France were spotted in the Channel.
Two Border Force vessels, the Dover lifeboat and a Coastguard aircraft are working alongside French authorities.
Twenty-seven people in several boats were intercepted on Saturday after attempting the journey.
It comes as Home Secretary Priti Patel visited Calais to discuss the situation with her French counterpart.
Ms Patel signed a deal on immigration and border management that will establish a joint intelligence unit with France focused on tackling people smugglers.
More than 2,400 people have crossed the English Channel from France in small boats this year.
Speaking this week, the home secretary said the crossings were a “complicated issue” but the Channel has become “far too viable for criminals”.
One of new French Interior Minister Gerald Darmanin’s first moves in his role was to order the dismantling of several makeshift camps and move hundreds of migrants out of Calais.
On Saturday, 21 migrants in three boats were brought back to France – including four in a boat that capsized.
And the Home Office confirmed that six migrants were detained by police in Dover after arriving in a small boat and handed over to immigration officials.
A note on terminology: The BBC uses the term migrant to refer to all people on the move who have yet to complete the legal process of claiming asylum. This group includes people fleeing war-torn countries, who are likely to be granted refugee status, as well as people who are seeking jobs and better lives, who governments are likely to rule are economic migrants.