Angry Eurostar passengers have vented their frustrations on Twitter after an incident at Dagenham Docks station left hundreds of travellers stuck on trains that were not moving for more than two hours.
ITV News has learnt the delays were caused by a person on a bridge who was threatening to jump.
Eurostar confirmed trains had slowly started moving again shortly after 11pm.
Eurostar trains have been suspended because of a trespasser on the UK part of the railway, the operator has said.
The incident near Dagenham Docks station is causing delays to services in and out of London St Pancras International. It is not known when services will resume.
A man who tried to climb onto the roof of a Eurostar train is fighting for his life in hospital after getting an electric shock from an overhead power line.
The Egyptian was reportedly trying to jump from one train to another at the Gare du Nord station in Paris when he suffered serious burns.
Eurostar said traffic was interrupted on Wednesday after an accident led to a power cut.
Eurostar has said it expects normal service to resume tomorrow but has warned passengers to expect trains to be "exceptionally busy".
It apologised to travellers for the disruption and said it was working through outstanding ticket changes.
Meanwhile Eurotunnel tweeted its services, which were also affected by the disruption, were now operating to schedule from the UK and from Calais.
Eurostar will be running a reduced service for the rest of today as striking French ferry workers who were blocking the Channel Tunnel have been cleared from the site.
A spokesman from Eurostar told ITV News that the following trains will run today:
St Pancras - Paris 9036 – 15.31 9040 – 16.22 9050 – 19.01 9054 – 20.01
Paris – St Pancras 9047 – 17.13 9053 – 18.43 9059 – 20.13 9063 – 21.13
St Pancras - Brussels 9140 – 15.04 9158 – 19.34
Brussels – St Pancras 9149 – 16.56 9161 – 19.52
Passengers with a ticket for these trains should arrive at the station as normal, allowing plenty of time for check-in.
Those who were booked onto a train cancelled today will need to rebook their ticket before travelling, through Eurostar.com
The P&O Ferries boss has launched a withering attack on the French and British government as well as Eurotunnel. P&O Ferries chief executive Helen Deeble blamed Eurotunnel for putting passengers in the middle of an industrial relations battle by not securing the jobs of workers involved.
A blockade by striking ferry workers in Calais has left "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."
Eurotunnel has said it "deplores" the protest which saw tires burned on tracks in a blockage that meant services through the Channel Tunnel had to be suspended.
The Channel Tunnel has been shut again because of protesting MyFerryLink workers, Eurotunnel and French traffic supervision body Bison Fute said.
Angry workers have blocked the entrance to the tunnel, setting fire to tyres, a witness told Reuters.
Eurotunnel have blockaded Calais for a second day after a court rejected their bid to extend a charter contract with Eurotunnel. The MyFerryLink workers say the court decision jeopardises hundreds of jobs at their company.