NEW YORK (AP) – A free concert by pop band Hanson and up-and-coming Canadian rapper Drake was cancelled on Tuesday after twice as many people as anticipated showed up and many became unruly, police said.

The show started at about 6 p.m. with an opening act at Pier 17 on Manhattan's South Street Seaport, a popular summer locale for concerts. Hanson, the Tulsa, Oklahoma, brothers behind the 1997 hit 'Mmmbop', and headliner Drake, whose album 'Thank Me Later' debuted on Tuesday, were to appear on stage soon after.

Organisers were anticipating about 10,0000 people but nearly 20,000 showed up, police said.

Many people climbed roofs and started throwing bottles, as concertgoers smashed together toward the stage, police said.

Witness Tamika Johnson told the Daily News newspaper: "People in the front started leaving because they were getting crushed."