France was facing transport meltdown on Tuesday as a tense standoff between unions and the government over labour reform saw oil refineries blocked and a fifth of its fuel pumps run dry.

Just three weeks before the Euro 2016 football tournament and days before the British half-term holidays, when thousands of motorists cross into France, at least seven out of eight of the country's refineries were cut off, fuel shortages looked set to worsen and a string of rail and air strikes are looming.

Hostilities commenced before dawn on Tuesday when police launched a raid to “liberate” an oil refinery near the southern port of Marseille held by strike picketers. Officers fired tear gas and water cannon to oust protesters blocking the Exxon Mobil refinery and terminal at the Fos-Sur-Mer site.

They met stiff resistance as picketers hit back by lobbing paving slabs and setting crates and tyres on fire, lightly injuring seven officers.

However, unionists said they had successfully managed to block the country's other refineries, along with several fuel depots.

One in every five of the country's 12,500 petrol stations were either completely dry or out of one type of fuel, a week after oil workers first went on strike, according to Alain Vidalies, the transport minister.