The late Australian actor Heath Ledger was awarded one of his country's most prestigious film awards on Saturday for his final role as The Joker in the Batman movie The Dark Knight.

Ledger, 28, who died of an accidental overdose of painkillers and other medicines in his New York apartment 11 months ago, was posthumously awarded the AFI (Australian Film Institute) international award for best actor.

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Guests at a packed awards ceremony in Melbourne's Princess Theater rose to their feet clapping, but with some in tears, to pay tribute to the actor who was nominated for an Oscar for his role as a taciturn gay cowboy in 2005's Brokeback Mountain.

"It has been without a doubt the most difficult year, losing such a loved family member," said his sister Kate, fighting back tears as she accepted the award alongside Ledger's parents.

"We are so proud of him and humbly accept this award on behalf of his beautiful daughter (Matilda) who we will cherish forever."

The AFI, celebrating its 50th-annual award ceremony, paid tribute to Ledger, describing him as "ground-breaking actor trapped in the body of a leading man".

"He was the untamed spirit many of us wish we could be. May the legend live on," an AFI tribute said.

Cate Blanchett won the equivalent award for women for her role in Elizabeth: The Golden Age. A drama about a teenage boy learning to live with an autistic brother won the night's top award for best film.

The Black Balloon, the favorite to win best film and nominated in 11 categories, beat The Jammed, The Square and Unfinished Sky for the coveted award.

The film, which opens in the United States this month, picked up various other awards including best supporting actor and actress for Luke Ford and Toni Collette, while director and co-writer Elissa Down won best direction and original screenplay.

Unfinished Sky, a rural romantic drama which received 10 nominations, received the award for best adapted screenplay and its leading actors, William McInnes and Monic Hendrickx, took home the awards for best lead actor and actress.

In television, the critically acclaimed crime drama Underbelly about the Melbourne gangworld dominated the night, winning six of eight awards for which it was nominated, including best TV drama series.