Rescue services were faced with chaotic scenes in the Channel, as a female migrant died and dozens of others were rescued, while more than 600 others made it to the UK.
A mayday call was issued just before 2pm after one migrant boat got into difficulties just as it arrived in UK waters.
Maritime sources tell GB News a "significant number" of migrants ended up falling overboard and into the Channel.
The Border Force vessels Hurricane and Volunteer were already on scene, waiting to carry out what should have been a routine pick up of migrants from two dinghies as they crossed the line into British waters.
Instead, they scrambled to pull multiple migrants to safety, as lifeboats from Dover and Walmer were also dispatched to the scene, along with a Coastguard plane and a helicopter.
The female migrant was pulled from the sea in an unresponsive state. She was winched aboard the Coastguard helicopter and flown back to Dover.
But despite efforts to resuscitate her, she was declared dead.
The migrant boat was one of two that had been under escort by the French border patrol ships Ridens and Minck.
Migrants are seen wrapping themselves in blankets after arriving in Dover
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GB News filmed as those migrants, wrapped in blankets, were taken off the Volunteer and led to the Border Force processing centre for medical checks.
The incident comes shortly after GB News revealed that at least 500 migrants have crossed into UK waters so far, with more boats launching from the French coast.
Almost 1,100 had also entered the UK illegally via small boats on Saturday alone.
As Cabinet colleagues describe new Home Secretary Shabana Mahmood as "hard as nails", people smugglers appear to have ignored her tough stance.
On Ms Mahmood's first full day in office, smugglers sent 1,097 migrants towards the UK.
Dozens can be seen departing the vessel
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Today, before dawn, they launched several migrant rafts from beaches around Calais and Dunkirk.
The illegal migrant activity has now moved much further south, below Boulogne, where more boats have just set off on their journey.