The film opens in 3,661 theatres across the US and has sold a record number of advance tickets there and in several other countries, analysts have said.

It is expected to shatter box-office records on release.

Meanwhile DVD pirates are preparing to flood the market with illegal copies of the film, authorities said.

'Phenomenal' sales

And a US consulting film has calculated the film's release has cost $627m (£342m) in lost productivity.

Consulting firm Challenger, Gray and Christmas said the buzz about the film would prompt many people to skip work for daytime screenings.

"Already, we were looking at huge opening weekend audiences who have long anticipated the grand finale in this 28-year journey," said John Challenger.

He predicted the loss to companies based on absenteeism caused by the other prequels, the proportion in full-time work, and their average pay.

Fans may skip work for daytime screenings, a consultant says

"Of course, these estimates are probably on the conservative side in light of the great reviews the moving is receiving," he said.

Several overseas markets have already reported advance takings higher than the box office grosses of the previous prequels, The Phantom Menace and Attack of the Clones.

The massive interest in the film, which was premiered in Cannes on the weekend, has prompted many midnight screenings.

"We are seeing phenomenal advance ticket sales in many territories," Paul Hanneman, Fox International's exec VP for sales and strategic planning, told US magazine Variety.

One theatre chain said its advance sales were 60% higher than for The Lord of the Rings - The Return of the King, which took US$124m (£67.66m) in its first five days in North America.

"It is gigantic," said Fandango executive Art Levitt. "For those who are waiting for the opening bell to ring on summer, it's rung loud and clear."

Pirate sleeves found

Sleeves for pirate Revenge of the Sith DVDs and discs with director George Lucas' introduction have been seized in London - but the film itself has not yet been found.

"It's telling us that the bad guys are preparing for a mass influx of this product," said the Federation Against Copyright Theft's (Fact) Jim Angell.

Star Natalie Portman and director Lucas at the film's Cannes premiere

Some 400 sleeves made in preparation for the discs were seized in a police raid in Woolwich, south London, on Friday.

And discs with a 10-minute long introduction by Lucas were found on Brick Lane, east London, on Sunday.

Mr Angell said Fact had been "on alert mode" and "keeping a sharp eye" out since premieres and press preview screenings began.

"Fortunately for Fox, the distributors of the film, we haven't received any counterfeit film as yet."

But pirates had "some sort of business acumen and they want to flood the market as soon as possible", he added.

The raids came as the DVD industry launched its latest anti-piracy campaign, against selling pirate DVDs in workplaces.

More than a quarter of people who buy pirate DVDs do so in their places of work, according to The Industry Trust for IP Awareness.