A United States judge declared a mistrial today in Bill Cosby's sexual assault case after the jury announced that they remained deadlocked and unable to reach a verdict against the fallen television star.

It was a stunning development for the 79-year-old pioneering black entertainer who had risked spending the rest of his life in prison if convicted on drugging and molesting a woman at his home 13 years ago.

Around 60 women have publicly accused Cosby in recent years of being a serial sexual predator alleging that he drugged and assaulted them over a span of 40 years across the United States.

But 44-year-old Andrea Constand's alleged assault was the only criminal case brought against him as most of the alleged abuse happened too long ago to prosecute.

But if the man once adored by millions as 'America's Dad' escaped conviction today, prosecutor Kevin Steele said that he intended to seek a re-trial as authorised in such cases under the law.

The seven-man, five-woman panel had spent around 53 hours deliberating in Norristown, Pennsylvania, longer than the amount of time dedicated at the trial to testimony and legal arguments.

They first informed Judge Steven O'Neill on Thursday that they were deadlocked, but were instructed to return to their deliberation room and try harder, without being given a deadline or timeframe.

Less than 48 hours later, and working into the weekend on a Saturday -- the 11th day of the trial -- the panel informed the judge that they were still deadlocked on all three counts against Cosby. -- Agencies