ROME (Reuters) - A nationwide power blackout struck Italy in the dead of night on Sunday, unleashing chaos, stalling lifts, stranding travelers, but causing no known disasters.

Practically all the country's 57 million people were hit, a failure similar in scale to last month's collapse in the U.S. Northeast and Canada -- though, coming on a weekend night, its initial impact was less dramatic and less economically damaging.

"It's chaos, and until the electricity comes back on it will continue to be chaos," said policeman Fabio Bragazzi, 21, at Rome's main Termini train station where passengers, among some 30,000 stranded across the country, slept on the ground.

Disbelief was heightened by uncanny coincidence -- it was the fourth major Western blackout in two months, after cuts in North America, parts of London, and Scandinavia.

CROSS-BORDER CUTS

Officials first blamed it on the breakdown of two big lines from France, which provides critical supplies and up to a fifth of Italy's needs at night, during severe storms.

But they later said lines from Switzerland and Austria also failed, apparently helping to trigger the blackout, which also hit an adjacent Swiss region.

"It was an exceptional, extraordinary event," Andrea Bollino, chairman of Italy's grid operator GRTN, told Reuters.

France's grid operator RTE said the blackout started with four successive line failures between Switzerland and Italy.