'21' holds onto US box office top spot

Robert Luketic's real-life drama 21 has held onto the US box office top spot for a second week.

Children's adventure movie Nim's Island lands at number two, while George Clooney's romantic comedy Leatherheads enters at third.

The only other new entry was Carter Smith's horror thriller The Ruins, which goes straight in at number five.

The top ten in full:

1. (1) 21 - $15,337,418
2. (-) Nim's Island - $13,210,579
3. (-) Leatherheads - $12,682,595
4. (2) Horton Hears a Who! - $9,115,987
5. (-) The Ruins - $8,003,241
6. (3) Superhero Movie - $5,417,920
7. (4) Tyler Perry's Meet the Browns - $3,418,255
8. (5) Drillbit Taylor
9. (6) Shutter - $2,830,336
10. (7) 10,000 B.C.- $2,797,409