Hundreds of refugees and migrants have stormed a motorway leading to the port at Calais in desperate attempts to board lorries heading for the UK.

Riot police were sent to the incident near the “Jungle” camp on Wednesday morning, firing tear gas and attempting to force asylum seekers off the road.

The busy A216 was closed in both directions after clashes started at around 10am (9am GMT), causing P&O to warn of delays and diversions for passengers trying to reach its ferries.

Calais refugees share personal stories

Local newspaper La Voix du Nord reported that up to 400 people climbed fences on to the motorway and attempted to stop traffic so they could hide on lorries.

Clashes reportedly broke out, seeing migrants throw rocks and projectiles at riot police, including one that injured a lorry driver.

An officer told the newspaper that the situation was “serious”.

“I have been on this assignment for a month but this time even worse,” he said. “There are big, big crowds. They want to stop HGVs but the HGVs are increasingly refusing to stop.

The road has since re-opened and delays around Calais were clearing.

Thousands of asylum seekers fleeing conflict and repression in the Middle East and Africa are believed to be camping in Calais in the hope of reaching the UK, although numbers have declined since the "crisis" in August.

Many are in the so-called Jungle, where aid organisations have described squalid and unsanitary conditions that have worsened with the onset of winter.

In pictures: Calais crisis intensifies Show all 20 1 /20 In pictures: Calais crisis intensifies In pictures: Calais crisis intensifies Calais crisis French gendarmes try to stop migrants on the Eurotunnel site in Coquelles near Calais In pictures: Calais crisis intensifies Calais crisis French gendarmes try to stop migrants on the Eurotunnel site in Coquelles near Calais Getty Images In pictures: Calais crisis intensifies Calais crisis A migrant climbs a security fence of a Eurotunnel terminal in Coquelles near Calais In pictures: Calais crisis intensifies Calais crisis A migrant climbs a security fence of a Eurotunnel terminal in Coquelles near Calais In pictures: Calais crisis intensifies Calais crisis French gendarmes block migrants along a road to prevent them access to train tracks which lead to the Channel Tunnel in Frethun, near Calais In pictures: Calais crisis intensifies Calais crisis Policemen try to prevent migrants from reaching the Channel Tunnel operated by Eurotunnel in Coquelles near Calais In pictures: Calais crisis intensifies Calais crisis A policeman faces migrants trying to reach the Channel Tunnel operated by Eurotunnel in Coquelles near Calais In pictures: Calais crisis intensifies Calais crisis A policeman tries to stop migrants on the Eurotunnel site in Coquelles near Calais In pictures: Calais crisis intensifies Calais crisis Migrants who managed to pass the police block on the Eurotunnel site climb over a fence to make their way towards the boarding docks in Coquelles near Calais In pictures: Calais crisis intensifies Calais crisis Migrants are seen near a Channel Tunnel train in Coquelles near Calais In pictures: Calais crisis intensifies Calais crisis Migrants trying to reach the Channel Tunnel run past policemen in Coquelles near Calaisa In pictures: Calais crisis intensifies Calais crisis Migrants step over the fence as they try to catch a train to reach England, in Calais In pictures: Calais crisis intensifies Calais crisis A migrant climbs a security fence of a Eurotunnel terminal in Coquelles near Calais In pictures: Calais crisis intensifies Calais crisis Migrants warm themselves with a fire as they attempt to access the Channel Tunnel, in Calais In pictures: Calais crisis intensifies Calais crisis An Afghan flag flies above makeshift shelters at a site dubbed the "new jungle", where migrants trying to cross the Channel to reach Britain have camped out around the northern French port of Calais In pictures: Calais crisis intensifies Calais crisis Migrants build a makeshift shelter around the northern French port of Calais In pictures: Calais crisis intensifies Calais crisis Migrants build a makeshift shelter In pictures: Calais crisis intensifies Calais crisis Migrants walk in a makeshift camp in Calais In pictures: Calais crisis intensifies Calais crisis A driver climbs on his truck as he waits to cross the English channel, in Calais In pictures: Calais crisis intensifies Calais crisis Migrants walk along the roadside while a French policeman secures the area as lorries queue in Calais

Volunteers have been building shelters and staffing limited facilities but the French government has now started work on a new camp to house 1,500 people in larger tents, while shipping containers are also being repurposed.

At least 13 asylum seekers have died trying to cross from Calais to Dover this year, with some being electrocuted by power cables in the Eurotunnel, hit by trains, falling or being killed in car accidents.