PHITSANULOK: A man firing two guns killed three staff members at Radio Thailand's Phitsanulok station, and wounded another, on Wednesday morning.

Gunman Wim Sonsuk, an electrician, began his rampage about 11am, police said. 

Armed with two handguns, he shot dead three staff members -- the station director, an electrician and a technician.

Another technician was shot and wounded.

Mr Wim then waited at the radio station for police to arrive.

Police said Mr Wim also had a knife with him and had planned the shooting in advance.

The station director had tried to run away but was chased down and killed at the back of the building. He was the last person to be shot.

Investigators were still questioning witnesses and collecting evidence from the scene. 

The shooter's motive was not yet known. 

Mr Wim was in custody and under close watch to ensure he did not try to take his own life.