The French government announced an "action plan" Friday to counter attempts by migrants to cross the Channel to Britain by sea, which will include an increase in coastguard patrols and ramped up surveillance in ports.

These new measures will be in addition to a joint action plan announced on December 31 by the French and British government, according to a statement from the French interior ministry.

An increase in crossings by asylum-seekers, mostly Iranians, has caused alarm in Britain and put the Conservative government there under pressure to provide a response. 

"This plan should enable us to end these crossings," the French statement said, adding that they were "not only illegal but also extremely dangerous.

"It's in our interest, as well as the United Kingdom's, to do everything to prevent new networks (of people smugglers) developing which would likely attract irregular migrants to our shores again," it added. 

A British navy ship was patrolling the Channel on Friday in addition to other French and British coastguard boats which watch over the 33 kilometres of sea that separate France and Britain at its narrowest point.

French Interior Minister Christophe Castaner is to travel to London soon to discuss the joint Franco-British plan, Friday's statement added.

The promise of extra patrols and police checks in ports aimed at stopping migrants trying to cross the Channel contradicts an earlier statement on Friday by French government spokesman Benjamin Griveaux.

Griveaux told a news conference that "there is no requirement to increase any further the resources there which are working very well and are proving their worth."

He downplayed the severity of what British Home Secretary Sajid Javid has termed a "major incident" by comparing the number of arrivals in Britain to the number of people crossing the Mediterranean by sea.

"We are not talking about the same level at all," Griveaux said.

A total of 504 people, the vast majority in the last two months, attempted to cross the Channel to Britain in 2018, with 276 successful in reaching British waters, according to the latest figures from the French interior ministry.

Data from the UN's refugee agency showed that 55,756 people crossed the Mediterranean to Spain in 2018.