A gunman has shot and killed six people and wounded two more during a shooting spree in the US.

The suspected shooter was arrested without incident at the Skagit County Sheriff's office after leading Washington state troopers on a chase down a major highway.

Police did not identify the suspect, but said he was from Alger, Washington, a small town 75 miles north of Seattle.

Local media said the suspect has a history of mental illness and a criminal past.

Police spokesman Sergeant Robert Goetz said: "We have multiple crime scenes with multiple victims. This incident is very large in scope."

One of the victims was a sheriff's deputy, who was responding to an emergency call reporting a person had been shot.

Police later discovered the bodies of two construction workers a few blocks from where the deputy and the first victim were shot.

Police also found another victim in the vicinity and later found a person shot dead in a car off a motorway.

The incident is the latest in a series of mass shootings over the last few years in the US, which is estimated to have the world's highest civilian gun ownership rate.

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