A woman was hospitalized in serious condition. Authorities said she was fighting for her life Tuesday night.
Authorities began receiving 911 calls about a shooting at Clackamas Town Center about 3:30 p.m. PT.
Detectives said the gunman, described only as an adult male, died from a self-inflicted gunshot wound. Witnesses said the gunman looked like a teenager and was wearing a bullet-resistant vest and mask. He was reportedly carrying an assault rifle.
As many as 60 shots were fired. Authorities said there was no gunfire inside the mall by law enforcement.
A motive for the shooting was under investigation.
Sheriff's officials said the shooter had been tentatively identified. They would not release the name until the identity was fully confirmed. It was not immediately known if the gunman had accomplices.
The names of the deceased were not released pending notification of next of kin.
In a news conference Tuesday night, sheriff's officials said about 10,000 people were inside the mall at the time of the shooting.
Police SWAT teams were moving methodically through the mall searching for anyone else who may be injured or hiding. Officials said hundreds of people had already been evacuated. The interior floor plan of the mall measures 1.4 million square feet, according to sheriff's officials. The mall was to remain closed Wednesday.
More than 100 law enforcement personnel responded to the shooting, including members of the ATF, FBI and local police agencies.
Officials assured the public that items such as strollers, purses, wallets and the like that were left behind in the mall were secure and would be allowed to be picked up later. They said a process would be determined, but that it was low-priority at this point in the investigation.
Holli Bautista, 28, said she was shopping in the Macy's when she heard a two or three pops that sounded like firecrackers. She said the Macy's opens into the food court area, where it was reported the shootings took place.
"I heard people running and screaming and saying 'Get out, there's somebody shooting,'" she said. "It was a scene of chaos."
She said hundreds of shoppers and mall employees started running, and she and dozens of other people were trying to escape through an exit in the department store.
"My thoughts and prayers are with the victims and their families," said Oregon Gov. John Kitzhaber in a statement. "I appreciate the work of the first responders and their quick reaction to this tragic shooting."
The Associated Press contributed to this report.