A TGV high speed train passes behind razor-wire fencing close to the Channel Tunnel site on which a sweat shirt is stretched over the barbs to protect asylum seekers who climb over the fence in Calais, northern France, July 29, 2015. [Photo/Agencies]

"The nightly pressure is more than what a concession-holder can reasonably handle," it said, calling on Britain and France to act.

Cazeneuve and his British counterpart Theresa May met on Tuesday to discuss the crisis, and May was due to chair a meeting of the government's emergency "Cobra" committee in London later on Wednesday.

Britain has agreed up to 7 million pounds ($10.9 million) of extra funding to help increase security at the tunnel's French terminal at Coquelles, officials said.

British authorities said they had agreed with the French to work together on returning the migrants to their countries of origin, particularly in West Africa, although no details were given about how this would work.

The crisis at Calais has had a knock-on effect on road traffic on the British side and caused huge delays for freight lorries as well as holidaymakers trying to reach the continent.

Some sections of the British media and some politicians have criticised France's handling of the crisis, though the government has stressed the importance of cooperation.

"There's no point trying to point fingers ... of blame," British Prime Minister David Cameron told reporters during a visit to Singapore, adding he was "very concerned" about events in Calais.

"It's about working with the French, putting in place these additional security measures, adding in the investment where that's needed.... We know how important this is," he said.