French police on Tuesday said they would probe a shocking video showing violence against migrants in the northern port town of Calais, from where they hope to cross to Britain.

The amateur footage shows policemen repeatedly beating and kicking migrants who had been hiding in trucks en route to Britain, hoping to secure a better life across the English Channel.

The policemen also use tear gas to immobilise some of their targets, and force others down onto the ground with their knees.

The amateur footage surfaced less than four months after Human Rights Watch condemned police abuse of migrants in Calais, and slammed the slow response of the French government to their poor living conditions.

The French police directorate on said it launched an investigation on Monday into the violence.

"The exact circumstances of this intervention will be rapidly examined... and any failure to apply the ethical rules will be punished," the police said in a statement on Tuesday.

Prosecutor Jean-Pierre Valensi of Boulogne-sur-Mer near Calais told AFP he had  summoned the police's internal inspection body over the footage, which shows acts that are "liable to be classed as criminal... if they are proven".

The Calais Migrant Solidarity group, which released the video on its website, says it dates back to May 5, a day after French Interior Minister Bernard Cazeneuve visited Calais.

Nan Suel of French NGO Terre d'Errance told AFP: "I agree that the policemen are in an impossible situation... but nothing justifies these violent acts."

"The first word the migrants learn in French is 'degage'," which means "go away", she added.

Police at Pas-de-Calais said more than 300 migrants -- double the average 150 a day -- arrived on Tuesday on roads leading to the Channel tunnel.

With its rail and sea links to Britain, Calais has long been a hub for migrants, but numbers have soared since spring 2014, as more and more people flee conflict and repression in Sudan, Syria, Eritrea, and Ethiopia.
Source: AFP