Police say a trolley bus involved in the parade celebrating the Seattle Sounders' MLS Cup victory struck and injured a bicycle officer on Tuesday.

Images from television news cameras overhead showed other officers tending to the injured officer, who appeared to have suffered a leg injury. Witnesses told KOMO news that the officer was pinned underneath the trolley.

Four trolley buses were carrying players, coaches, supporters and politicians past thousands of jubilant fans en route to a rally at Seattle Center on Tuesday afternoon when the accident occurred.

Police also said two people had been arrested for attempting to board the trolleys.

At intersection of Queen Anne and Mercer street where what appears to be a police bike is crunched underneath a Sounders trolley. pic.twitter.com/kRnqHn1mqa - Evan Bush (@evanbush) December 13, 2016

Crowds lined the streets Tuesday chanting "Seattle ... Sounders," waving signs and cheering as a procession of trolley buses carried players and coaches along Fourth Avenue.

Police officers walked alongside the buses, as players leaned out to shake hands with fans and sign autographs. At one point, defender Roman Torres could be seen thrusting the trophy into the air.

The sea of green and blue colors made its way down Fourth Avenue toward Seattle Center, where a rally will celebrate the team's dramatic victory on penalties.