Harvey Weinstein's 2020 conviction for sexual assault and rape was overturned by New York's highest court, reopening the landmark case that launched the #MeToo movement and highlighting the challenges of holding powerful men accountable.

In a bitterly divided 4-3 decision on Thursday, the state Court of Appeals said the trial judge made a critical mistake by letting women testify that Weinstein assaulted them, even though their accusations were not part of the charges he faced.

The court said the trial judge compounded the error by letting Weinstein be cross-examined on a broad range of "loathsome" conduct, including bullying and fits of anger toward associates, that portrayed him in a "highly prejudicial" light.

"It is an abuse of judicial discretion to permit untested allegations of nothing more than bad behaviour that destroys a defendant's character but sheds no light on their credibility as related to the criminal charges," Judge Jenny Rivera wrote for the majority.

"The remedy for these egregious errors is a new trial," she added.

Weinstein, 72, has been serving a 23-year sentence in a prison in upstate Rome, New York.

He is not expected to be freed immediately, as he also faces a separate 16-year prison term in California after being convicted there last year for the 2013 rape of an actress at a Los Angeles hotel.

Manhattan District Attorney Alvin Bragg, whose predecessor Cyrus Vance brought the New York case, will decide whether to retry Weinstein.

"We will do everything in our power to retry this case, and remain steadfast in our commitment to survivors of sexual assault," Emily Tuttle, a spokesperson for Bragg, said in an email. (Reuters)