US civil rights epic "Lee Daniels' The Butler," which is generating serious Oscar buzz, topped the North American box office for a second straight weekend, industry figures showed Monday.

The drama, based on the real-life story of an African American butler who witnessed decades of US history from within the White House walls, earned $16.5 million, industry tracker Exhibitor Relations said.

Critics have hailed the performances of Forest Whitaker in the title role and Oprah Winfrey as his wife, giving the actors a leg up in the early race to the Academy Awards, the climax of Hollywood's annual awards season scheduled for March 2 next year.

"We're the Millers," a dark comedy about pot-smuggling starring Jennifer Aniston as a stripper, moved up from third to second place with $13 million in ticket sales.

"The Mortal Instruments: City of Bones," a teen-romance demon thriller about a girl who discovers dark secrets from her family's past, debuted in third place at $9.3 million.

Another debut film, action disaster comedy "The World's End," opened in fourth place with $8.8 million in sales.

The newcomer pushed animated film "Planes," a spin-off of the hugely successful "Cars" franchise, into fifth place at $8.6 million, just ahead of "You're Next," a horror flick about a family weekend gone awry, which debuted in sixth place with $7 million.

Science-fiction thriller "Elysium" dropped to seventh place at $6.9 million.

"Percy Jackson: Sea of Monsters," an adaptation based on the book series by Rick Riordan about a schoolboy who is the son of the Greek god of the sea, Poseidon, made $5.3 million, dropping to eighth place from sixth last week.

In ninth spot was superhero action comedy sequel "Kick-Ass 2," which earned $4.4 million.

Woody Allen's acclaimed drama "Blue Jasmine," which stars Cate Blanchett and Alec Baldwin, rounded out the top 10 with just under $4 million.