Image copyright PA Image caption Theresa May visited Calais with French Interior Minister Bernard Cazeneuve

The migrant crisis could shift from Calais to other ports, Home Secretary Theresa May has said.

Mrs May said she was "well aware of the possibility of displacement" of the issues at Calais, and was "looking at" security at ports including Dunkirk.

She spoke as the UK and France agreed a deal further improving security around Calais.

She said ministers were also in talks with Belgium and the Netherlands about security at their ports.

Commons Home Affairs Committee chairman Keith Vaz echoed Mrs May, highlighting the "dangers of the domino principle" and saying that closing one route "will only mean the problem moves to another port".

He said agreements needed to be in place with countries across Europe's north coast to prevent that.

'Resistant to abuse'

Migrants camped in and around Calais have been making nightly attempts to reach the UK, often by boarding lorries heading for the port or the Eurotunnel.

Mrs May, who toured the Eurotunnel site in Coquelles earlier, said it had been a "difficult summer" with high levels of migrant activity and strike action in Calais.

But she said joint efforts with the French government were working.

She said France and the UK would also work with other EU states to try to ensure there were "fully functioning external borders and an asylum system that is resistant to abuse".

French Interior Minister Bernard Cazeneuve said asylum seekers should be welcomed "with dignity", but illegal immigrants would not be tolerated.

Image copyright AFP/Getty Images Image caption A demonstration by migrants brought cars to a halt on a motorway in Calais

The joint deal sets out measures including an extra 500 police from the UK and France, additional freight search teams, including sniffer dogs, and UK-funded flights to return migrants to their home countries.

The plan also includes a "control and command centre" that will be jointly run by British and French police and will "relentlessly pursue" people-smuggling gangs, Mrs May said.

The UK will pay £3.5m (five million euro) per year over two years towards the measures in the deal, and the Home Office said this was in addition to money previously pledged.

The six-page joint declaration says UK Border Force officers will continue visiting migrant camps to "correct any misapprehensions" about life in the UK and provide a "more dissuasive and realistic sense of life for illegal migrants" there.

Meanwhile, a demonstration by migrants - chanting "we are not animals" and "open the borders" - brought cars to a halt on a motorway and a road near the so-called "Jungle" camp.

BBC reporter Amanda Kirton said police were sent to the motorway which overlooks the camp to disperse the crowd, and tear gas was used.

About 3,000 migrants are thought to be camped in Calais.

Media playback is unsupported on your device Media caption Thousands of migrants have tried to reach the UK in recent months, as Tomos Morgan reports from Calais

Migrant crisis

Image copyright Reuters

Migrants who are camped in Calais are attempting to reach the UK by crossing the Channel

Eurotunnel has described "nightly incursions", with sometimes hundreds of migrants attempting to breach security at once

The situation in Calais is part of a wider migration crisis in Europe - caused largely by people fleeing war and oppression in countries such as Syria, Afghanistan and Eritrea

More than 240,000 migrants have crossed the Mediterranean already this year, arriving on the shores of Greece and Italy

Read more: Why is there a crisis in Calais?