'District 9', an alien thriller set in an apartheid society divided between humans and space creatures, landed at the top of the North American box office on Sunday, initial weekend figures showed.

The film, which touches on themes of racism and corporate greed, earned $37-million in its first week of release, according to box office tracker Exhibitor Relations.

It tells the story of a race of extraterrestrial refugees who are granted asylum in South Africa but have to fight off attempts by a nefarious corporation seeking to harness their powerful alien technology.

In second place, down from the top spot was 'G.I. Joe: The Rise of the Cobra'. The action movie based on the popular toy franchise pulled in $22.5-million over the weekend.

New release 'The Time Traveler's Wife', starring Rachel McAdams as the wife of a man with a genetic anomaly that means he moves back and forward through time involuntarily, earned the number three spot, with box office receipts of $19.2-million.

Falling two places to number four was 'Julie and Julia', a movie that tells the story of famed cook Julia Child, and Julie Powell, a woman who tries to cook a recipe a day from Child's most famous cookbook for one year.

In its second week in theaters, the feature starring Meryl Streep and Amy Adams, earned $12.4-million.

Also falling two spots was 'G-Force', an action-comedy about a crack squad of guinea pig spies, which fell to number five, earning $6.9-million.

At number six was 'The Goods: Live Hard, Sell Hard', a comedy starring Jeremy Piven and Ed Helms as employees of a struggling car dealership, which pulled in $5.4-million in its first week in theatres.

In its fifth week of release, 'Harry Potter and the Half-Blood Prince', the sixth installment of the franchise, fell three spots to number seven, earning $5.2-million.

The feature, which sets the stage for the final confrontation between the boy wizard and his arch-nemesis Lord Voldemort, has taken in $283.9-million since its release.

At number eight was 'The Ugly Truth', starring Katherine Heigl as a romantically-challenged producer looking for love, which took in $4.5-million in its fourth week in theatres.

In at number nine was 'Ponyo', an animated Japanese movie about a goldfish who befriends a human boy. The new release took $3.5-million in box office receipts.

Down one spot from last week was '(500) Days of Summer', a whimsical romantic movie that fell to number 10, with earnings of $3.0-million.