Two key parts in the next Harry Potter film are up for grabs, according to Hollywood studio Warner Brothers, which has announced an open casting call.

The studio says the casting sessions in London will be held for the roles of Lavender Brown and Tom Riddle. Aspiring actors between the ages of 15 and 18 are required for Harry Potter and the Half-Blood Prince, the sixth book in the series.

Harry Potter and the Half-Blood Prince was released in July 2005.
(Canadian Press)

Brown is the girl who ends up dating Harry's best friend, Ron. The studio says Lavender is a "pretty and lively girl who loves to be the centre of attention" and "reacts in an extreme way to everything."

Tom Riddle is a darker character described as "not a warm boy, but he is very charismatic. Both staff and children are probably all a little scared of him."

Auditions for Lavender Brown take place July 1 and for Tom Riddle on July 8 at the Earl's Court Exhibition Centre.

This is not the first time the studio has sought non-professional child actors. A similar open call landed Evanna Lynch her first film role — as Luna Lovegood in Harry Potter and the Order of the Phoenix, which hits theatres in July.

Then 14, the Dublin-based Lynch captured the attention of the casting director over 15,000 other hopefuls.

Lynch, who is now 16, has described herself as a rabid fan of the wizard-in-training books by J.K. Rowling.

"Watching the movies, I always thought it would be so cool to be in Harry Potter and to make that your job," Lynch told the Basingstoke Gazette in England.

"I wanted to go for Luna. I'm not one to sit around and wait for fate to do things so I got my friends and made a tape. They played Harry and Ron — they were very good about it, very patient — and I sent that away."