Pro-euthanasia film The Room Next Door has won the Venice Film Festival's best film award.

The feature film starring Tilda Swinton and Julianne Moore took the prestigious Golden Lion award on Saturday.

Earlier in the week, the Pedro Almodovar-directed film received an 18-minute standing ovation after it premiered at the festival - one of the longest in recent memory.

Accepting the award, 74-year-old Spanish director told the audience: "I believe that saying goodbye to this world cleanly and with dignity is a fundamental right of every human being."

The film sees Swinton play a war correspondent suffering from terminal cancer. She asks her old friend, played by Moore, to be at her side as she takes her own life.

Almodovar said he made the film to communicate his belief euthanasia should be available around the world.

"It is not a political issue, but a human issue," the Oscar-winner Almodovar said. The film is his first feature film in English.

Almodovar also thanked Moore and Swinton for their performances.

"This award really belongs to them, it's a film about two women and the two women are Julianne and Tilda."

President of the jury, French actor Isabelle Huppert, said the film tackled important issues thoughtfully and without melodrama.

The Room Next Door is poised to be one of the most talked-about films of awards season.

The 81st edition of the world's oldest film festival wrapped up on Saturday night, with international celebrities flocking to Venice's red carpet.

Among the other award winners was Nicole Kidman who won the best actress award for her role in Babygirl, in which she plays a high-powered CEO putting her career and family on the line to begin an affair with her much younger intern.

Although Kidman was in Venice for the film's premiere last week, the Australian actress did not attend the awards ceremony after learning her mother had died.

"My heart is broken," Kidman said in a statement read out onstage on her behalf.

"I'm in shock, and I have to go to my family. But this award is for her. She shaped me, she guided me, and she made me," she said.

France's Vincent Lindon received the best actor award for French language film The Quiet Son, about a family torn apart by extreme-right radicalism.

The best director award went to American Brady Corbet for The Brutalist, recounting the tale about a Hungarian architect and Holocaust survivor played by Adrien Brody, who seeks to rebuild his life in the US.

Queer with Daniel Craig playing a gay drug addict, and the Maria Callas biopic Maria, starring Angelina Jolie as the celebrated Greek soprano did not get any awards.

The festival marks the start of the awards season.