Some 69 migrants - including 10 children - were found trying to cross the English Channel early on Tuesday morning.
While air temperatures hovered around eight degrees Celsius (46F) in Dover, five small boats were intercepted by Border Force as they made their way towards the United Kingdom.
The 69 people presented themselves as Iranian, Iraqi and Uzbek nationals, the Home Office said, adding that it is working closely with French authorities and that patrols on French beaches have been doubled.
In the first incident on Tuesday, at about 12:45am (00:45 GMT), a Border Force vessel intercepted a boat which was carrying a group of eight men who said they were Iranian nationals, the Home Office said.
Then, at about 3:35am, another boat was intercepted, this time carrying a group of 18 people, made up of 14 men, two women and two children.
At 5.10am, Border Force intercepted a boat carrying nine people - seven men and two children who also said they were Iranian nationals.
In the fourth incident, a boat carrying 23 people was intercepted at about 5:30am.
That group was made up of 14 men, five women and four children who have presented themselves as Iranian, Iraqi and Uzbek nationals.
In the fifth incident at around 7:45am, a Border Force vessel intercepted a boat carrying a group of 11 people - made up of eight men, one woman and two children who said they were Iranian nationals.
The people have all been medically assessed and will now be interviewed by immigration officials.
A Home Office spokesman said: "Those attempting to cross the Channel in small boats are putting their lives in grave danger and the ruthless criminals who facilitate crossings do not care about the risk to life.
"We are working closely at all levels with the French authorities to tackle this dangerous and illegal activity."
Newly elected Dover and Deal MP Natalie Elphicke said on Tuesday she has sought an urgent meeting with the UK's interior minister and called for more to be done in mainland Europe to prevent dangerous crossings.
"The French have been given tens of millions of pounds of British hard-earned taxpayer money to stop illegal departures from their shores," said Elphicke. "I want to know where the money has gone.
"Because while much has been done, it is clear there is more to do."
