Power has now been restored in Rome and in northern Italy, notably the Veneto and Friuli regions, and the cities of Turin and Milan.

The country was plunged into darkness early today after a mammoth power outage, which caused havoc on public transport nationwide, with only the island of Sardinia unaffected.

The national rail network was thrown into chaos, with up to 30,000 passengers stranded in around a hundred trains, while hospitals switched to emergency generators.

In Milan and Rome, passengers were trapped in the city's underground system as escalators ground to a halt.

French and Italian electricity officials said the blackout, which lasted more than five hours, had been triggered by a sudden interruption of power supply from France.

The Italian public service broadcaster's first TV channel, RAI 1, interrupted its normal broadcasting for live coverage.

The head of the civil protection services, Guido Bertolaso, told RAI 1 at around 8.00am (local time) the situation was 'completely under control' and that it was hoped the power supply could be completely restored to normal by the early afternoon.

The blackout put an early end to Rome's first 'White Night', an extravaganza of cultural events, inspired by a similar event staged last year in Paris, whose mayor Bertrand Delanoe was a guest of his Rome counterpart Walter Veltroni.

Italian Industry Minister Antonio Marzano said the 'exceptional incident' had been caused by an outage of two power lines carrying electricity from France to Italy.

France's national grid on Sunday confirmed that two high tension powerlines supplying Italy were cut briefly early Sunday.

Power was cut at 3.25am, 'probably because of stormy conditions in the zone,' Réseau de Transport d'Electricité said in a communique.

Earlier a spokesman for the Italian electricity company ENEL there had been a sudden shortfall of around 3,000 megawatts from around 3.00am.

But French source blamed an Italian failure to reopen power cables connecting France and Italy following an incident on the lines.