Panicked customers rushed to the exits when a gunman opened fire Tuesday at a mall outside Portland, Oregon. Some people huddled behind store counters and hid behind racks of clothing. The mall's Santa dropped to the ground.

Three people were killed, including the shooter, said Lt. James Rhodes of the Clackamas County Sheriff's Office. The shooter died of a self-inflicted gunshot, he said. One person suffered a traumatic injury.

A witness told CNN he tried to help a wounded woman who was lying on the ground by a cell phone store.

"She had apparently been shot in the chest, and I couldn't get her turned over to help her," said Antonio Charro, who had been shopping at the mall with his daughters. "There was no one around. She wasn't breathing."

Witnesses said a masked man with a gun headed toward the food court at the two-story Clackamas Town Center mall, located about 11 miles southeast of downtown Portland.

A woman told CNN affiliate KOIN that she saw a man wearing a hockey mask jogging through Macy's and wielding an assault rifle.

"Everyone ran toward the exits at that point to get out," she said.

Outside Macy's, gunshots echoed where a man portraying Santa Claus was snapping photos with kids.

"I heard two shots, then 15 or 16 more shots," he told CNN affiliate KGW. "I hit the floor."

The sounds of gunfire rang out through the mall, witnesses said.

"We heard one gunshot. It sounded like something fell," David Moran, an employee at the mall, told CNN. "Then it was a matter of two or three seconds, and then it was just rapid gunfire."

Customers and employees alike started running for the exits, Moran said.

"I thought I was going to die," he said. "The gunshots were so loud, it was very scary. ... Kids were crying. Parents were crying, too."

Inside Sears, some customers burst into tears as word spread of the shooter going store to store, Christina Fisher told KOIN.

"We were told to stand in a group by the top of the escalators and stay away from the windows out of the aisle. ... We stood there for probably a good 20 minutes," she said. "All of the sudden, somebody came through with a radio, yelling 'get down!'"

A group of customers inside Sears watched television news reports about the shooting inside the store's entertainment center, witness Tylor Pedersen told CNN affiliate KGW.

Pedersen said he heard about the shooting when people ran into the store, saying they had heard shots fired in the middle of the mall.

"I didn't think it was real at first until I saw the reactions on their faces," he said. "They were serious."

Authorities put the mall on lockdown as they searched for the shooter, witnesses said.

Later, they escorted people outside.