Soul star Isaac Hayes in hospital

Hayes gained a popular following voicing the Chef in TV's South Park

Soul singer Isaac Hayes, best known for the hit theme tune to the 1971 film Shaft, is being treated at a Memphis hospital for exhaustion.

"He was just overworked," his longtime songwriting partner David Porter told the local Commercial Appeal newspaper. "He's doing much better."

Hayes, 63, is also the voice of Chef in the animated TV show South Park.

He won a best original song Oscar in 1972 for Shaft - the first African American to win the award.

The musician picked up a Golden Globe for best original score in the same year.

He and Porter established a successful songwriting team in the 60s, with hits including Sam and Dave's Soul Man.

He also features in the recent film Hustle & Flow, opposite the Golden Globe nominated actor Terrence Howard and will appear on US TV series That 70s Show later this year.

The 63-year-old star performed last week in Atlantic City, New Jersey and Tunica, Mississippi. He was inducted into the Rock and Roll Hall of Fame in 2002.

Hayes' agent was unavailable for comment.