The Port of Calais has been closed this evening after a storm of migrants broke into the harbour.
More than 100 migrants stormed the site and some have even made it on to ferries in a desperate attempt to reach Britain.
It came after a protest organised by French leftists to support migrants living in squalid conditions in the northern city of Calais drew around 2,000 people, according to organisers.
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The Port of Calais has been closed after more than 100 migrants stormed the harbour, pictured, in a bid to get to Britain
It followed a 2,000-strong protest against the living conditions in migrant camps at the French city that turned into an escape attempt
A tweet showing what is believed to be a group of migrants after they boarded the Spirit of Britain ferry
Water canons, pictured, have been used on board the ship in an effort to get the migrants to disembark
P&O has confirmed it is running at a delay of between 90 minutes and two hours after migrants boarded the Spirit of Britain
The protest on Saturday came as British Labour leader Jeremy Corbyn visited the region, which is temporary home to about 4,000 migrants camped out in hopes of finding a better life in Britain, across the Channel.
Long lines of cars and lorries are now building up outside the port and the incident has led to fears of travel chaos ahead of planned closures to the Eurotunnel from 9pm tonight.
The tunnel is shutting so an overnight safety exercise can take place and all services will be suspended, with the last UK departure at 9.20pm and the first departure leaving the UK at be 6.20am tomorrow and from France at 7.20am.
The Mayor of Calais Natacha Bouchart closed the port and said around 50 migrants made their way on to the P&O-operated vessel. Police are at the scene and water canons have been used on board the ship to try to get the group to leave.
Meanwhile, a statement tweeted by P&O said: 'The Port of Calais is resolving a security incident. As a result our vessels are subject to delay of between 90 and 120 minutes.'
In a video filmed by a bystander, crowds can be heard cheering as migrants try to force their way through the fence.
According to Reuters, port staff said some of the migrants have left the Spirit of Britain voluntarily and the rest will be removed by police if necessary.
Migrants are filmed breaking into the port, pictured, by a bystander and then making their way towards the ferry
Crowds can be heard cheering as the migrants bash their way against the fence, pictured, before forcing it open
Long lines of lorries and cars are building up outside the port with the Eurotunnel set for a planned closure overnight from 9pm
Danish firm DFDS Seaways called the incident a 'migrant invasion', adding the port would be reopened once police had cleared them out.
Numerous migrants have died trying to make the crossing illegally.
Witness Ben Ferguson said: 'Demonstrators broke police lines & headed to the port. In spite of clouds of teargas a group prised open fence b4 (sic) crowd followed.'
A statement from the Port of Dover said the French port was experiencing 'migrant activity' which had caused disruption to services.
It read: 'The Port of Calais is currently experiencing migrant activity which has caused disruption to ferry services. Therefore services to and from Calais via the Port of Dover are affected, but DFDS Seaways services are still running to Dunkirk as normal.
'The Port of Dover remains open for business, but the duration of this disruption to services remains unknown.'
Migrants, pictured running towards the port, are reported to have had tear gas fired at them by French police officers
A group is believed to have ripped open a fence in order to get access to the harbour in Calais, pictured
The incident comes hours after UK Labour leader Jeremy Corbyn visited the region and said more had to be done to help migrants deal with 'disgraceful conditions'
Some people from Britain were present at the demonstration while others carried banners saying 'refugees welcome here'.
But France is under pressure from Britain to secure the region and the French premier said this week that Europe cannot welcome everyone.
Mr Corbyn's visit comes amid a growing urgency over the migrant crisis, with French prime minister Manuel Valls warning the huge influx is putting the European Union's future in 'grave danger'.
During his visit, Mr Corbyn was given a tour of the site meeting refugees and aid workers before speaking of the 'dreadful situation' faced by people camped in the swamp-like conditions.
He said: 'What I'm trying to achieve here is to understand the nature of the refugee crisis that's facing the whole of Europe.
It is understood the group that invaded the port is larger than 100 people, disrupting services at the harbour
It is unknown exactly how many migrants were able to make their way onto the Spirit of Britain, pictured, but more than 50 are believed to be aboard, according to the Mayor of Calais
Mr Corbyn visited camps in Calais and Dunkirk today talking to migrants about living conditions and lack of doctors, education and food
'Ultimately we deal with the situation by dealing with the problem at its source, which are the wars and conflicts.
'Also, there are the human needs of people. We have got people here who have been here for months, if not longer than that, with no proper education, no access to doctors, no access to dentists, limited access to food - in very cold, very wet conditions.
'These conditions are a disgrace anywhere. We as human beings have to reach out to fellow human beings.'
Mr Corbyn said Britain should be part of a pan-European effort to help the people affected by the crisis.