Sajid Javid told migrants thinking of crossing the English Channel not to risk their lives, as he watched the work of border patrol teams off Dover.
The home secretary defended his call to declare a major incident last week, saying there had been a steep increase in the numbers making the journey.
In response, the UK is to step up the number of vessels patrolling the area.
Mr Javid urged people not to travel and – if seeking asylum – to do so in France, or elsewhere on the continent.
Twelve migrants were found on the Kent coast last week, bringing the total number of people to have reached the UK by boat since November to 239.
French police said they stopped 14 migrants attempting to cross the channel from Boulogne on Tuesday, the latest in a growing number of people intercepted by the French authorities in the past month.
As part of a joint action plan agreed with France, Mr Javid – who cut short his holiday to deal with the issue – has ordered two UK Border Force boats to be redeployed from overseas to patrol the Channel.
Only one of the five Border Force cutters – specialist boats which the force describes as being capable of rescuing several migrant boats at the same time – had been working in the Straits of Dover.
The two being brought back are currently in the Mediterranean, where they have been taking part in Operation Frontex, the pan-European effort to deal with much larger migration flows from North Africa and the Middle East to Italy and Greece.
Speaking during a trip to the UK’s largest port, in which he went out on patrol on HMC Searcher, the home secretary said the intensified operation would “make a big difference” in protecting human life, as well as securing the UK’s borders.
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He defended escalating the UK’s response, saying 80% of the 539 people who had attempted to cross the Channel in small boats in 2018, had done so since October.
“We have seen a real step-change in attempts in the last three months,” he said.
“People should not be taking this very dangerous journey and, if they do, we also need to send a very strong message that you won’t succeed.”
The vast majority of asylum seekers making the journey should instead, he said, be approaching the authorities in France or elsewhere on the continent.
“If you are a genuine asylum seeker, you could have done that in another safe country. We need to send a strong message that these gangs preying on you and selling you a false prospectus will not succeed.”