Almost 400 migrants were intercepted crossing the Channel to the UK in small boats on one day.
The latest numbers mean at least 1,892 migrants have arrived so far in September, more than in all of 2019.
The 393 people were found in 26 small boats on Tuesday.
Clandestine Channel Threat Commander Dan O'Mahoney said French authorities also prevented a further 10 crossings, with almost 100 more people detected on the beach and inland.
The government said a total of 1,835 migrants crossed the Channel in 2019.
Despite extra resources deployed to the Dover Strait, Border Force officials said they were busy for more than 13 hours dealing with crossings along more than 65 miles of coastline between Kent and East Sussex.
Dozens of people believed to be migrants were seen arriving in Dover harbour wrapped in blankets and wearing lifejackets.
They included children, with one in pink waterproofs who had to be carried.
Many had to queue before they were allowed to disembark from Border Force boats because of the volume of arrivals.
Border Force cutter Seeker, pictured 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 operating 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.
Home Secretary Priti Patel has said she aims to make crossing "unviable," adding that "the only way to do this is by intercepting and returning the boats back to France".
She said that French authorities do not routinely turn back boats due to differing interpretations of what action is legal under international maritime law - which prioritises the preservation of life at sea.
The UN Refugee Agency has said it was "troubled" by plans to intercept and return boats, adding that "deployment of large naval vessels to deter such crossings and block small, flimsy dinghies may result in harmful and fatal incidents".