US comic Bill Cosby has been charged with sexual assault in Pennsylvania over an incident that took place in 2004, a prosecutor said Wednesday -- the first criminal charges filed against the actor after dozens of women claimed abuse.

"Mr Cosby is charged with aggravated indecent assault. This is a felony of the first degree," Kevin Steele, assistant district attorney for the state's Montgomery County, told reporters.

Cosby was to be arraigned on the charge of aggravated indecent assault later Wednesday.