CORSICA was sealed off by land and sea yesterday, leaving thousands of tourists stranded, as a sailors’ strike developed into a full-scale confrontation between nationalists and the French authorities.

Airports were closed and ferry terminals blocked, cutting the Mediterranean island off from mainland France and raising fears of a food shortage.

About 50,000 visitors are thought to be on the island at present, 8 per cent of whom, the Corsican Tourist Board estimates, are British.

On Thursday dozens of tourists had to be put up overnight in a gymnasium in Ajaccio when they found themselves unable to leave Corsica. Hundreds are looking for accommodation elsewhere on the island after their return journeys were cancelled.

The dispute, sparked by French plans to privatise the Corsica-Mediterranean Ferry Line (SNCM), has led to clashes between police and demonstrators. It plunged further into violence when a rocket was fired at the office of Prefect Pierre-René Lemas, the State’s representative on the island.

Although no one was injured in the attack, which was condemned by President Chirac, police fear that it could signal a fresh round of violence on an island that seen three decades of explosions and murders.

M Lemas said: “I can’t help making a link between (the rocket) and the industrial action. Some people are trying to exploit the conflict for their own reasons.”

The sea route to mainland France has been closed since Wednesday, when paramilitary gendarmerie commandos stormed a ferry that had been taken over by striking seamen.

Alain Mosconi and Félix Dagregorio, two of the sailors who are accused of hijacking the Pascal Paoli ferry, were remanded in custody yesterday. M Mosconi’s two brothers, Jean-Marc and Patrick, who are also alleged to be among the ringleaders, were released on bail.

The Union of Corsican Workers has responded by blocking ports on the island and France’s hard-left Confédération Générale du Travail has taken similar action in Marseilles. Yesterday 42 ships were trapped in the southern French port and another 20 were stranded offshore, at an estimated cost to the French economy of €476 million (£333 million) a day.

In Corsica, Bastia airport was shut down completely and Ajaccio airport partially closed as ground workers and firemen joined the strike.

The blockades are likely to lead to shortages within days, according to officials. Long queues formed outside petrol stations, and bakers said that they were already running out of yeast. The authorities set up a crisis group to handle remaining stocks of medicines, liquid oxygen and gas.

Dominique de Villepin, the Prime Minister, has been widely criticised for failing to consult unions before announcing the sale of a ferry line that has cost French taxpayers almost £1 billion in subsidies since 1991.

In an editorial, the newspaper Libération said: “The Prime Minister has commited a gross mistake. He’s been caught out like a novice in his first important conflict.” M de Villepin, who initially intended to privatise fully the SNCM, has backtracked and now says that the Government will keep a 25 per cent stake. But unions want the company to remain under state control.

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