ALGER (Washington) - A SHOOTING rampage on Tuesday afternoon in northwest Washington has left six people dead, including a sheriff's deputy, the State Patrol said. A suspect in the shootings has surrendered.

Two people were wounded during the violence in Skagit County, including a state trooper who reportedly was grazed in the arm by a bullet.

A man was arrested after turning himself in at the Skagit County sheriff's office in Mount Vernon, Trooper Keith Leary said.

He was not immediately identified but Mr Leary said he is known to authorities as 'someone with a mental illness.'

The dead were found at multiple crime scenes. They included the deputy shot while responding to a call and a second person killed at the same location near the small town of Alger; two construction workers found shot nearby, and a third body found a few houses away, Leary said.

Authorities were investigating any connection among those sites.

A motorist was shot and killed on Interstate 5 as the suspect fled south.

The wounded included a motorcyclist who was shot in the arm at a Shell gas station in Alger and the trooper hit as the suspect raced along I-5.

After the shootings in the Alger area, the armed man raced south on Interstate 5 at speeds in excess of 140kmh, with troopers, sheriff's deputies and Mount Vernon police in pursuit, Mr Leary said.

The civilian motorist was shot and killed and the unidentified trooper was grazed by a bullet along I-5 near a rest stop, Mr Leary said. The trooper was treated for non-life-threatening injuries.

The victims were not immediately identified.

The first shootings were reported shortly after 2pm on Tuesday and the suspect was in custody by about 4.30pm.

State Patrol troopers temporarily closed all southbound lanes of I-5 north of Burlington for a period on Tuesday evening, backing up traffic for miles, as they investigated that crime scene. -- AP