Striking French ferry workers have blocked the Channel Tunnel again causing services to be suspended, Eurotunnel said.
Both Eurostar and Shuttle services were halted because of fire on the tracks at Calais caused by demonstrators.
As Calais was plunged into chaos for the second time in a fortnight, the UK government described the situation as "completely unacceptable".
A Eurotunnel spokesman said: "Services through the Channel Tunnel are currently suspended until further notice due to action by the Maritime Nord union who are also blockading the port of Calais.
"Eurotunnel deplores the actions of this union which have severely disrupted cross channel traffic over the past week. Eurotunnel calls on the governments of both Britain and France to bring an end to this industrial action and to restore order in the Calais region."
It is understood that this happened at 12.45am when protesters broke in to the Eurotunnel site and blocked the track with burning tyres.
They cut their way through fences in to the Eurotunnel site.
Earlier the British Government described the disruption caused by the industrial action as "completely unacceptable".
A statement said the British and French governments were working closely to see services return to normal as soon as possible.
It added: "Passengers on both sides of the Channel intending to travel through either Dover or Calais should check with their chosen operator before they travel.
"Operation Stack is in operation on the M20 and road users are advised to follow the signs in order to minimise disruption."
Kent Police warned that the port of Calais would be closed until Thursday while Eurotunnel described the situation as "grim", particularly for freight traffic.
Ferry services to and from Dover in Kent have been hit by the strike, which started at the northern French port at 2.20pm yesterday.
Striking ferry workers are blockading the French port to all users, meaning the "the local environment is in chaos ... there is gridlock", according to a Eurotunnel spokesman.
He said that in recent days the pattern of migrant activity has spread from attacking trucks on motorways to trying to access the terminal.
He said: "There are migrants everywhere which means we have to control the trucks before they get to the site."
Crew members and catering staff on MyFerrylink services announced a strike after Eurotunnel, which owns the ships, sold the cross-channel service to rival operator DFDS.
The sale came after a competition authority ruling and left up to 600 jobs, including 70 in Dover, under threat.
MyFerrylink, which runs 16 crossings from Dover to Calais, was due to officially stop all services from a minute past midnight on Thursday. The firm could not promise that services will restart before then.
P&O Ferries chief executive Helen Deeble said: "This has left thousands of holidaymakers and lorry drivers stranded without adequate facilities - even though our employees at the port have done their level best to keep them supplied with food and water."
Ms Deeble blamed Eurotunnel for putting passengers in the middle of an industrial relations battle by not securing the jobs of workers involved.
In a statement she added: "Let me be clear: the buck stops with the French Government. They have shown that they can move swiftly to stop any disruption at the tunnel. But they have effectively abandoned any attempt to maintain security at the port of Calais, which makes a nonsense of European co-operation.
"And when is the British Government going to stand up to ensure that we can all get to mainland Europe safely and securely? Every day that the disruption lasts costs UK Plc millions of pounds."
She said that P&O Ferries employs thousands of people on both sides of the Channel and "this damaging and dangerous industrial action is now putting those jobs at risk".