Image copyright Getty Images Image caption Erin Moran also starred in a spin-off series Joanie Loves Chachi

US actress Erin Moran, best known for playing Joanie in 1970s sitcom Happy Days, has died, aged 56.

Police said an emergency team in Indiana responded to a call on Saturday afternoon and found her dead.

The cause is not yet known.

Moran also starred in the show's spin-off series Joanie Loves Chachi, which began in 1982. She played Joanie Cunningham, the younger sister of lead character Richie.

Richie was played by Ron Howard, who has been among those posting the first tributes online.

Image copyright Twitter / Ron Howard

Henry Winkler, who played The Fonz in the series, also shared condolences on Twitter.

Image copyright Twitter / Henry Winkler

Moran joined the Happy Days cast in 1974 when she was 13.

She also made appearances in Murder She Wrote and The Waltons.

In recent years, she was reported to be living in an Indiana trailer park.

In 2010, she joined various Happy Days co-stars in filing a lawsuit against television network CBS, claiming they were owed money from merchandising revenues.

The suit was settled in 2012, with the actors each receiving a payout of $65,000 (£50,000).

They originally asked for $10m.