Huge numbers of migrants reached the UK on Tuesday in a flurry of small boat crossings.
A wave of people took advantage of calm seas in the Channel, with hundreds intercepted as they headed towards Britain.
At least 393 migrants made the crossing aboard 26 boats, the Home Office confirmed.
It brings the number who have made it to the UK in September to at least 1,880, according to analysis by the PA news agency.
This is roughly the same number believed to have crossed in the whole of 2019, and a pledge by Home Secretary Priti Patel to make the route “unviable” is in “tatters”, according to a charity.
The Home Office’s Clandestine Channel Threat Commander Dan O’Mahoney met the French ambassador on Tuesday to discuss the crisis.
Even with extra resources deployed to the Dover Strait, Border Force was busy for more than 13 hours dealing with crossings along more than 65 miles of coastline.
Dozens of people thought to be migrants were seen arriving in Dover harbour wrapped in blankets and wearing lifejackets.
They included children, including one in a pink jacket who was too young to walk.
Many had to queue before they were allowed to disembark from Border Force boats because of the volume of arrivals.
Border Force cutter Seeker, making a rare visit to the inner harbour to drop off the migrants, was part of a scaled-up contingent of vessels that were busy in the Channel on Tuesday.
The agency had at least five boats in operation on Tuesday: cutters Seeker and Searcher and patrol boats Hunter, Speedwell and Eagle.
A police boat was also operating in the Channel along with a coastguard helicopter and the RNLI.
The agencies were kept busy along miles of coastline across East Sussex and Kent for several hours.
September has been the busiest month for crossings on record, with a week still to go.
In France, authorities rescued at least 88 people trying to cross to the UK.
Patrol vessels were busy for more than 14 hours as several boats carrying migrants were intercepted off the coast.
On land, French law enforcement destroyed a number of boats to prevent further crossings.
Mr O’Mahoney said: “Yesterday I met with the French ambassador to the UK where I reiterated the urgency to tackle the issue.
“We discussed how best the UK and France can use new tactics and operational activity to stop the boats leaving French shores in the first place.”
Bella Sankey, director of humanitarian charity Detention Action, said: “Priti Patel’s claim she would make Channel crossings unviable lies in tatters as this has been the busiest month on record.
“This dangerous situation is not sustainable but desperate refugees will continue to risk their lives as long as the Government refuses to offer safe passage to the UK for those fleeing persecution.
“Unless the Home Secretary changes tack she will look neither tough nor compassionate and will please no one.”