HOLLYWOOD (AFP) -- The Oscars kicked off Sunday with a historic early triumph for South Korea's black comedy thriller "Parasite" -- tipped to battle war epic "1917" for the night's top prize -- as winners including Brad Pitt struck a political note.

Hollywood's biggest night began with a vibrant musical medley, which addressed a swirling row over the lack of minorities and female directors on the star-studded nominee list.

"We celebrate all the women who directed phenomenal films and I'm so proud to stand here as a black, queer artist," singer Janelle Monae said pointedly as she led the spirited opening number with Billy Porter.

"Parasite" writer-director Bong Joon-ho earned a raucous ovation as he and co-writer Han Jin-won scooped the first ever Asian win for best original screenplay.

"We never write to represent our countries," said Bong. "But this is (the) very first Oscar to South Korea. Thank you."

The film, about a poor South Korean family infiltrating a wealthy household, is expected to battle "1917," Sam Mendes's innovative and personal World War I movie, for best picture.

"1917," about two soldiers crossing no-man's-land on a desperate mission -- filmed to appear like one continuous shot -- won for best cinematography and sound mixing, and is also in the running for other prizes.

But it missed out on the production design prize to Quentin Tarantino's "Once Upon a Time... in Hollywood."

Pitt won his first acting Academy Award for his supporting turn in Tarantino's film, using his speech to address President Donald Trump's recent impeachment trial.

"They told me I only have 45 seconds up here, which is 45 seconds more than the Senate gave John Bolton this week," he said.

Continuing the political theme, "American Factory" -- the first film from Barack and Michelle Obama's production house, about a Rust Belt factory reopened by a Chinese billionaire -- won best documentary.

"Working people have it harder and harder these days and we believe that things will get better when workers of the world unite," said co-director Julia Reichert.

Best adapted screenplay went to "Jojo Rabbit," the Nazi satire about a young boy corrupted by fascism during World War II who finds a Jewish girl living in his attic.

"I dedicate this to all the indigenous kids in the world who want to do art and dance and write stories," said writer-director Taika Waititi, who is of Maori origin.

"We are the original storytellers and we can make it here as well."

'We all miss him'

A-listers hit the red carpet under overcast skies at the Dolby Theatre, where a lavish, spiral stage featuring 40,000 crystals provided the glittering setting for the night.

The event's luxury and glamour contrast with the grief enveloping Los Angeles over the recent deaths of Golden Age film legend Kirk Douglas and Oscar-winning basketball star Kobe Bryant.

Veteran director Spike Lee arrived in a purple jacket with lapels bearing the number 24, worn by the Lakers icon who was killed in a helicopter crash two weeks ago.

"Tribute. Honor. Homage. We all miss him," said Lee.

Both Bryant and Douglas have been added to a hastily re-edited "in memoriam" montage honoring those Hollywood lost this year, with Billie Eilish expected to provide a moving musical accompaniment.

The record Grammy-winning singer, who will soon voice the new James Bond theme, is one of several high-profile musical guests on a night when all five nominated songs are being performed.

Rapper Eminem, who won an Oscar in 2003, made a surprise appearance on stage to perform his winning song "Lose Yourself" -- which was heavily bleeped out by censors.

Idina Menzel blasted out "Into the Unknown," the song from "Frozen II," with other singers who portray Elsa in foreign-languages versions of the Disney film.

Cynthia Erivo -- the only non-white acting nominee, who also sang and wrote the theme to anti-slavery biopic "Harriet" -- delivered a powerful performance.

Elton John, tipped to win for "(I'm Gonna) Love Me Again" from "Rocketman," was also due to perform.

Female directors

No female directors were nominated this year -- a theme referred to by several celebrities.

Natalie Portman, a best actress Oscar winner in 2011 for "Black Swan," literally wore her feelings -- she had their names stitched into the Dior cape she wore to the gala.

Those names included Lorene Scafaria ("Hustlers"), Lulu Wang ("The Farewell"), Greta Gerwig ("Little Women") and Marielle Heller ("A Beautiful Day in the Neighborhood").

Laura Dern, who won her first Oscar for best supporting actress in divorce tearjerker "Marriage Story," said backstage: "If I could give this Oscar to Greta Gerwig, I would do it right now."

In the main acting categories, Joaquin Phoenix and Renee Zellweger are believed to be far ahead of the competition for best actor and best actress.

Phoenix underwent a striking transformation to portray the title comic book supervillain in "Joker" -- as did Zellweger to play legendary Hollywood diva Judy Garland in "Judy."

The ceremony had no host for a second consecutive time, after last year's batch of bright guest presenters caused a trend-bucking uplift in TV ratings. (AFP)