Hundreds of employees are staging a wildcat strike over fears they will lose their jobs next month as part of a restructure at Calais.

A large number of migrants have been taking advantage of the strike action by trying to get into UK-bound cars and lorries backed up near Calais.

Eurotunnel said train services had been suspended in both directions due to the protesters on the tracks.

"We have been notified that protesters have gained access to rail tracks which means that for safety reasons Eurotunnel have to temporarily suspend their service," the firm said in a statement.

A spokeswoman told AFP news agency that protesters had "got onto the tracks and were burning tyres."

Eurostar announced mid-afternoon that services have been cancelled for the rest of the day.

It said trains stuck outside the tunnel would return to their original stations in London, Paris and Brussels.

Meanwhile, truckers have been forced to drive slowly or stop in queues on the A16 - the road that leads on to the Channel Tunnel - amid chaos created by the labour action. 

Desperate migrants were seen walking by the sides of motorways looking for opportunities to jump on to vehicles heading to the Port for Dover, with French police using tear gas to restrain some of the migrants.

The Foreign Office has updated its travel advice on France, urging travellers to keep their vehicle doors locked in slow-moving traffic and when unattended in Calais.

"There are large numbers of illegal migrants in and around Calais, who may seek to enter the UK illegally," it said.

"Although local police patrols have been reinforced, you should keep vehicle doors locked in slow-moving traffic and secure your vehicle when it is left unattended."

The strike began in the early hours of the morning, with workers burning tyres and hay bales on the road and closing the port.

Ferry services were badly affected and truckers were left at the mercy of migrants hoping for a ride across the Channel.

Haulier Chris Cary said he had been stuck at Calais since 3am and described the situation as "the worst I've ever seen."

He told Sky News that migrants "were trying your doors to get in the cab, trying to sneak under the axles on the trailers, trying to cut the locks and seals on the back of the trailers, even trying to climb on the roof of the trailers."

He added: "It's just getting worse out here.

"If they want to get in, they'll get in - they're armed and dangerous now."

The migrant problem in Calais has been growing steadily worse, with more than 3,000 gathering near the port since April, many fleeing countries such as Eritrea, Syria and Afghanistan.