American TV personality Bill Cosby has appealed a Pennsylvania state judge's refusal to dismiss a sexual assault case against him.

Dozens of women have accused the 78-year-old actor and comedian of sexual assault dating back decades, but the vast majority of cases have expired under statutes of limitations.

The small number of proceeding cases are being heard in civil court, except in Pennsylvania where Cosby is standing trial for the first time on a criminal sexual assault charge.

Cosby's appeal centres on a decision in Pennsylvania earlier this month by Judge Steven O'Neill who threw out an attempt by the actor's lawyers to have the case dismissed.

Cosby's lawyers filed their notice of appeal against that decision to the Superior Court of Pennsylvania on Friday.

The accusation against Cosby dates back to 2004, a matter that was originally settled by a civil suit in 2006.

Andrea Constand accused Cosby of forcing himself on her at his suburban Philadelphia home in 2004.

Prosecutors said he urged her to take pills and drink wine, leaving her unable to resist the assault.

In a deposition Cosby gave as part of the civil suit, he admitted giving Ms Constand a pill, but said all relations with her were consensual and accused her of lying about the assault.

Prosecutors reopened the case last year, claiming new evidence came to light in July.

Cosby's legal team argued that violated a 2005 agreement saying he would never be prosecuted over the allegation of assault made by Ms Constand.

The avalanche of accusations against Cosby have led television networks to back away from projects connected to him, and several universities have stripped him of honorary degrees.

On Friday, Cosby also appealed another decision in which the judge refused to disqualify the lead prosecutor from participating in an eventual trial.

AFP