TUKWILA - One teen was killed and another was seriously injured in a shooting Saturday afternoon inside Southcenter Mall as it was filled with thousands of pre-Thanksgiving shoppers, officials said.

"We just heard two big shots that just kind of echoed through the mall," said shopper Sara Dinsmore. "It was scary."

The gunman remains at large, but Tukwila police spokesman Mike Murphy said investigators anticipated identifying the shooter "soon" and then making an arrest.

Murphy said the shooting may have been gang related.

The mall, located off Southcenter Parkway, was placed under lockdown after the shooting and remained closed for the night. It was scheduled to reopen Sunday morning.

The two victims, believed to be 16 years old, were transported to Harborview Medical Center. One of them died there later. The other victim remains in serious condition with non-life-threatening injuries.

The shooter is described as a black man in his late teens or early 20s, about 5-feet-6-inches tall, 145 pounds, with lean build and short hair, with no beard or mustache.

He was last seen running through the mall, wearing a one-piece black outfit with red piping, Murphy said.

Murphy said the gunman used a pistol and fired multiple shots. He said at least four or five people had been detained and questioned about the shooting, but none of them was the shooter. He said some of them had been released.

As police searched for the shooter Saturday night, they allowed store employees and customers remaining in the mall to exit the mall in groups, Murphy said.

After the search was completed, Murphy said the assailant "must have got out with the crowd."

Other witnesses told KOMO News they heard at least three shots fired around 3:45 p.m. in front of the Forever 21 store near the mall's food court.

The gunfire sparked immediate panic, and people started running for the exits. Police and medics raced to the scene, lights flashing.

"Everybody ducked," said Hillary Young, who works at the mall. "All the employees ran in the back room. My co-worker was freaking out."

Shoppers were evacuated from the mall, and officers immediately began searching for the gunman.

It was not clear exactly what prompted the shooting, but witnesses said the teens involved were fighting before the gunfire.

"There was a couple different guys just fist fighting with each other," said Nick Bottomley, an employee at the mall. "And then one of them pulled out a gun and shot two of them."

The relationship between the shooter and the victims was not known.

Investigators with the Seattle Police Department's gang unit were at Harborview Medical Center on Saturday evening trying to speak with friends and relatives of the shooting victims.