Tweeted by @KATUNews: A picture from a Twitter user of shattered glass inside mall. #ClackamasShooting Photo

A gunman killed two people and wounded another before taking his own life Tuesday afternoon at Clackamas Town Center southeast of Portland.

The identities of the dead and wounded were not released Tuesday. A woman, estimated to be 18 years old, was taken by LifeFlight helicopter to OHSU Hospital in Portland where she remains in serious condition. She is expected to survive, authorities said.

In an 8:30 p.m. press briefing, Clackamas County Sheriff Craig Roberts said four SWAT teams searched the 1.4 million-square-foot mall for people who barricaded themselves for safety. An estimated 10,000 people were at the mall at the time of the shooting, he said.

Roberts said no motive had been determined yet.

Witnesses say a gunman armed with a semi-automatic weapon opened fire after entering the mall through the Macy’s department store entrance, then moved to the food court, where he continued shooting.

About 100 officers descended on the mall within minutes of the 3:30 p.m. shooting.

Lt. James Rhodes of the sheriff’s office said the gunman acted alone, something that was uncertain after the shooting. Asked if there was an accomplice, Rhodes said he did not know.