According to ratings data issued on Monday, Sunday's ceremony and performance show broadcast live on Walt Disney Co's ABC television was watched by an average 9.5 million viewers - down from 12 million in 2011.

The annual show also dropped 21 percent of its viewers compared to last year in the key 18-49 demographic most prized by advertisers.

The American Music Awards was up against stiff competition this year from football, but ABC said the telecast was the top TV show of the night with women and teens.

But big stars like Katy Perry, Rihanna, Adele and Beyonce did not turn up for the show as it celebrated its 40th anniversary as an alternative to the Grammys.

Bieber, 18, was the top draw on Sunday, winning three awards including artist of the year and performing live twice.

Korean Internet phenomenon Psy closed out the three hour ceremony with a rousing performance of his No.1 hit single "Gangnam Style", joined on stage with MC Hammer, one of the pioneering rappers from the 1980s.