Boris Johnson has told migrants not to attempt to get into Britain, warning anyone thinking of making the crossing “we will send you back”.
It comes after nearly 100 people took to small boats on Friday in separate attempts to traverse the English Channel.
The news prompted Home Secretary Priti Patel to seek talks with her French counterpart to address the crisis.
Mr Johnson told reporters on Friday: “Clearly the most important thing is to stop them coming across from France so we are working very closely with the French authorities.
“The point I would just make to people thinking of making this journey – one, it is very hazardous, you may think the weather looks great but it’s a very, very dangerous thing to do.
“The second thing is – we will send you back. The UK should not be regarded as a place where you could automatically come and break the law by seeking to arrive illegally.
“If you come illegally, you are an illegal migrant and I’m afraid the law will treat you as such.”
Authorities were called to at least seven incidents on Thursday involving 94 people who were trying to cross the water from France to get to the UK.
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The wave of attempted crossings continued on Friday – with UK authorities understood to have been called to the Kent coast near Lydd.
Earlier in the morning, the French coastguard said 24 migrants, reportedly including seven children and a woman, were also found trying to cross the Channel.
Dover MP Charlie Elphicke said on Twitter: “Only when migrants and traffickers alike know that they will not succeed in crossing the English Channel will this crisis come to an end.”
The news comes as Ms Patel prepares to hold talks with her counterpart, the French Interior Minister Christophe Castaner, to address the crisis in the wake of Thursday’s surge of reports.
The Home Office has now confirmed officials dealt with 64 people, including at least six children, who tried to reach England in small boats in six separate incidents on Thursday.
French authorities said it found 30 migrants, including 11 children, attempting to make the crossing that same day.
The Home Office said that the 30 people picked up by the French were all taken back to the continent.
The crossings came as official figures were published on immigration to the UK from the EU – with data showing the number of people offered asylum and other forms of humanitarian protection by the UK has risen to its highest level since 2003.
A Home Office spokeswoman said attempting such crossings was a “huge risk” and “the criminal gangs who perpetuate this are ruthless and do not care about loss of life”.
She added: “We have three Border Force cutters in the Channel and a joint action plan with France in place, including a co-ordination centre in Calais which assists with preventing illegal attempts to cross the border.
“Since January, we have returned more than 65 people who arrived illegally in small boats to Europe.
“We continue to monitor the ongoing situation and are working closely at all levels with French authorities on the issue.
“The Home Secretary will raise this issue with her French counterpart in the coming days.”