The suspect in a shooting at a Washington state mall that left five dead and sparked an intensive, nearly 24-hour manhunt is in custody, authorities said.

Washington state police identified the suspect via Twitter as 20-year-old Arcan Cetin, of Oak Harbor, Washington.

Authorities announced earlier that the suspect had been apprehended on Saturday evening. 

A gunman opened fire at the Cascade Mall,  in Burlington, Washington, on Friday night, killing four females and a man before fleeing.

Police officer Mike Hawley said he spotted Cetin on the street from a patrol car and immediately recognised him as the suspect in the shooting rampage.

"I literally hit my brakes, did a quick turn, I jumped out," Hawley said. "We both jumped out with our guns and he just froze."

Cetin was unarmed and was carrying a satchel with a computer in it. "He was kind of zombie-like," Hawley said.

No immediate charges were brought against Cetin, who awaited a court appearance Monday.

One of the victims was a 16-year-old girl. Sarai Lara's mother told The Seattle Times that her daughter had survived cancer as a young girl and was a happy student.

Evangelina Lara told the paper that she was shopping at the Cascade Mall with Sarai and her younger sister, but they split up; Sarai went to Macy's looking for pants.

The first emergency call came in just before 7pm on a busy Friday night at the Cascade Mall: A man with a rifle was shooting at people in the Macy's department store.

By the time police arrived moments later, four people were dead, and the gunman was gone, last seen walking towards a local highway.

A fifth victim, a man, died in the early morning hours on Saturday as police finished sweeping the 434,000-square-foot building. 

"This was a senseless act. It was the world knocking on our doorstep, and it came into our little community," Burlington Mayor Steve Sexton said at a news conference on Saturday.

As the small city absorbed the tragic news, critical questions remained, including the gunman's motive.

Surveillance video captured the suspect entering the mall unarmed and then recorded him about 10 minutes later entering the Macy's with a "hunting type" rifle in his hand, Mount Vernon police officer Chris Cammock said.

Authorities did not say how the suspect may have obtained the weapon - whether he retrieved it from outside or picked it up in the mall - but they believe he acted alone.

The weapon was recovered at the scene.

The identities of the victims - four women who ranged in age from a teenager to a senior citizen - were withheld pending autopsies and notification of family.

The identity of the man who was fatally shot was also withheld and may not be released until on Monday. 

US: Five killed in Burlington shopping centre shooting

Source: Agencies