PORTLAND, Ore. - Police are searching for those involved in an altercation on board a TriMet bus in northeast Portland on Tuesday.

The incident began just before 6 p.m. in the area of Northeast Martin Luther King Jr. Boulevard and Failing Street.

Police were dispatched to the area after a caller said several people were involved in a fight on a TriMet bus and they thought one or more of them might be armed.

When police showed up, they saw several people running from the bus and heard several shots fired.  Police say they tried to set up a perimeter to contain possible suspects, but did not have enough officers available quickly enough to do so.

One handgun was recovered from the scene and the Gang Enforcement Team was called in to begin an investigation. 

Police say it appears that no one was injured.