Space adventure "Gravity" and AIDS drama "Dallas Buyers Club" won early Oscars on Sunday, but suspense remained as the show moved towards its climax and the best picture award.

At the halfway point, "Gravity" had won five awards, all in technical categories, "Dallas Buyers Club" took two and "12 Years a Slave" earned a key acting prize at the Dolby Theatre in Hollywood.

The other main frontrunner, 1970s crime caper "American Hustle," was so far empty-handed, but the lead acting prizes, best director, screenplay awards and the coveted best picture prize were yet to be announced.

Leto, Nyong'o triumph'

As widely expected, Jared Leto won the best supporting actor Oscar for his portrayal of a transgender woman suffering from AIDS in "Dallas Buyers Club" on Hollywood's biggest night.

The actor and rock musician used his acceptance speech to send a topical message to people in troubled Ukraine and anti-government protesters in Venezuela.

"To all the dreamers out there... in places like Ukraine and Venezuela, I want to say, we are here. And as you struggle to make your dreams happen, to live the impossible, we're thinking of you tonight," Leto said.

"Dallas Buyers Club" also won the make-up and hairstyling award.

Lupita Nyong'o won the best supporting actress Oscar for "12 Years a Slave," earning a standing ovation as she took the stage.

A tearful Nyong'o paid tribute to her slave character Patsey, saying: "It doesn't escape me for one moment that so much joy in my life is thanks to so much pain in someone else's."

'Gravity' wins technical awards'

"Gravity," from Mexican director Alfonso Cuaron, won awards for visual effects, sound editing, sound mixing, cinematography and film editing.

Going into the evening, "12 Years a Slave," "Gravity" and "American Hustle" were frontrunners for the top prize, best picture.

The ceremony got underway after storm clouds lifted, allowing stars to hit the pre-show red carpet.

Briton Chiwetel Ejiofor, up for best actor for "12 Years a Slave," was among the A-listers who strutted their stuff, as did his co-star Nyong'o, stunning in pale blue Prada.

"It's quite a surreal moment," Ejiofor told CNN, adding that "it would be amazing" to win. But he stressed: "One of the proudest things... is that people have received the film in the spirit in which it was made."

On the acting front, Cate Blanchett is favorite for her turn in Woody Allen's "Blue Jasmine," while Matthew McConaughey is widely fancied to strike Oscars gold for his portrayal of homophobic HIV-positive AIDS activist Ron Woodroof in "Dallas Buyers Club."

'Very intense season'

On the eve of Hollywood's biggest night, "12 Years a Slave" scored a last-minute boost by winning best feature and best director for Briton Steve McQueen on Saturday at the Independent Spirit Awards.

But experts agree that all bets are off for the big prize of the night, the best picture Oscar, which will be handed out at the end of the show.

Host Ellen DeGeneres opened with a monologue making fun of the storms that hit California on the eve of the Oscars.

"It's been a tough couple of days for us here. It has been raining," she said, addressing the global audience. "We're fine. Thank you for your prayers," she dead-panned.

The 6,000 or so voting members of the Academy of Motion Picture Arts and Sciences cast their ballots over 12 days starting on Valentine's Day and ending on Tuesday.

'Too close to call'

The best picture race is so close that the winner could come down to only a few votes, under the Academy's preferential voting system. Under the rules, voters rank all nine nominated films.

They are: "American Hustle," "Captain Phillips," "Dallas Buyers Club," "Gravity," "Her," "Nebraska," "Philomena," "12 Years a Slave" and Martin Scorsese's "The Wolf of Wall Street."

Those with the least first-place votes are dropped, and their votes given to the next highest-ranked nominees. This continues until one movie has 50 percent plus one vote.

Cuaron is the frontrunner for the best director prize, and his star Sandra Bullock earned high praise for her work in the spectacular space drama, prompting some to suggest she could cause an upset in the best actress race.

The star-studded Oscars broadcast featured a performance by Irish rockers U2, playing their nominated song from "Mandela: Long Walk to Freedom," and Pink, who sang "Over the Rainbow" as part of a 75th anniversary tribute to "The Wizard of Oz."