Producer Jordan Horowitz holds up the card for the Best Picture winner Moonlight. [Photo/Agencies]

Accountants and Oscar officials on Monday were investigating how a meticulous procedure for announcing Academy Awards winners went disastrously awry, snatching a best picture victory from musical La La Land and handing it instead to Moonlight.

In a gaffe on Sunday that stunned the Dolby Theatre crowd in Hollywood and a television audience worldwide, presenters Warren Beatty and Faye Dunaway were handed the wrong envelope for the movie industry's top award.

The mistake was not rectified until the La La Land cast and producers were on stage giving their acceptance speeches. It was left to the musical's producer, Jordan Horowitz, to put things right.

"Guys, guys, I'm sorry. No. There's a mistake,” Horowitz said. "Moonlight, you guys won best picture. This is not a joke."

It took Pricewaterhouse Coopers, which has been overseeing Academy Awards balloting for 83 years, three hours to issue a statement confirming that Beatty and Dunaway "had mistakenly been given the wrong category envelope."

"We are currently investigating how this could have happened, and deeply regret that this occurred," the accountants said in a statement on Monday. The Academy of Motion Picture Arts and Sciences, which organizes the Oscars, had nothing to add.

An embarrassed Beatty carried the envelope in his hand to the glitzy Governor's Ball after the show, with the writing clearly saying "actress in a leading role." La La Land star Emma Stone had been awarded that Oscar moments before.

Brand management experts said it could take years for Pricewaterhouse Coopers (PwC) to recover.

"This is not advanced math. PwC had to get the right name in the right envelope and get it to the right person," said Tim Calkins, a marketing professor at Northwestern University, calling the blunder a "bit of a branding tragedy."