The shooting occurred at 8:40 p.m. Saturday and the investigation is ongoing.
"The investigation is ongoing, but detectives believe there are no outstanding suspects in this incident," said Portland Police Sgt. Greg Stewart.
One person has been detained for questioning, KATU-TV, Portland, reported.
Witness John Moller said it appeared as if a shooter targeted one of the bouncers, and then someone else retaliated.
Four people were taken to the hospital and two of them suffered life-threatening gunshot wounds.
The other two are expected to recover, KOIN-TV, reported.
The identities of the victims will be released Sunday pending family notification, the Oregonian reported.
Police said the community is not in danger.
In 2012, two men and one woman were arrested for allegedly killing Edward Ford Jr. in the club's parking lot.