"A very strong signal must be sent here in Calais that you can't pass the border that we manage together in the context of an absolutely exemplary cooperation between our two countries," Cazeneuve said when he and May visited the entrance of the Eurotunnel together.
They met representatives of both countries' police forces and aid workers who run a centre for the roughly 3,000 refugees from Africa, Asia and the Middle East who have gone to the town in the hope of crossing over to the UK.
Other measures in the agreement include:
- Extra French police and freight search teams equipped with dogs;
- Extra funds worth 31 million euros from Britain to beef up security and help humanitarian aid;
- Tighter security within the tunnel with Eurotunnel helping to increase the number of guards;
- An "integrated control room" covering the rail depots at Coquelles.
During July, when striking ferry workers picketed the port, Eurotunnel estimated that there were 2,000 attempts to break into the tunnel every night, although the number as gone down to 100-200 since.
Calais mayor Natacha Bouchart has called for the British government to pay France 50 million euros as compensation for the problems she says the migrants cause.
Cazeneuve was to go on to Berlin on Thursday.
Germany expects to handle a record 800,000 asylum-seekers this year.
A record number of migrants entered the European Union last month.