The entertainment world was preened and primed Sunday for the most fiercely contested Oscars show in decades, with three movies leading an impressive field for Hollywood's most highly coveted prizes.

After months of drought, a huge storm hit just in time for the Academy Awards, drenching the famous red carpet where A-listers will strut their stuff as Tinseltown's annual awards season comes to a climax, though the rain was expected to ease off into the evening.

The harrowing historical drama "12 Years a Slave," 3D space thriller "Gravity" and 1970s crime caper "American Hustle" are hotly tipped to take the top prizes.

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."

Jared Leto's role as Woodroof's unlikely transgender business partner has put him ahead of the field for best supporting actor, and Lupita Nyong'o could take home a statuette for her big-screen debut in "12 Years a Slave."

'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 Saturday at the Independent Spirit Awards.

McConaughey, Leto, Blanchett and Nyong'o took home the acting awards, further cementing their status as the ones to beat for the prized Oscar statuettes.

But experts agree that, while some categories may be seemingly settled, 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 86th Academy Awards ceremony hosted by US talk show host Ellen DeGeneres.

"It's been a very intense season because there's been so many good films," industry journal Variety's awards editor Tim Gray told AFP in the run-up to the Oscars.

"The very last envelope that's opened is going to be very suspenseful."

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.

But 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.

It has been a long awards season -- extended by the Sochi Winter Olympics, which bumped the Oscars from February into March to satisfy television demands.

And it has also been among the most grueling, partly due to the bumper crop of films vying for glory.

Topping nominations are "American Hustle" and Mexican director Alfonso Cuaron's "Gravity," with 10 nods apiece, followed by "12 Years a Slave," a true story of a free black man sold into slavery, with nine.

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.

But Australia's Blanchett remains the firm favorite in that category, despite a strong field also containing Meryl Streep ("August: Osage County"), Judi Dench ("Philomena") and Amy Adams ("American Hustle").

Starry, starry night

The star-studded Oscars broadcast will feature performances by Irish rockers U2, playing their nominated song from "Mandela: Long Walk to Freedom," and a first Oscars turn by veteran Bette Midler.

Sunday night's show will be preceded by the usual fashion extravaganza on the red carpet, as Tinseltown's finest parade along Hollywood Boulevard and into the Dolby Theatre.

Organizers hope rain doesn't affect the parade -- they were still scrambling Saturday to get everything in place amid a steady downpour, 24 hours before the curtain goes up.

A see-through tent covers the whole runway, and the carpet itself had a layer of plastic on it, but there was little disguising that rain had got through, with workers constantly mopping up.