Wichit Police were informed of the incident at about 2pm.
Kwannapa Patjirang, wife of the truck driver, explained that she was in the truck with her husband while they were travelling northbound on Chao Fa West Rd when they noticed a white Toyota Revo pickup being driven erratically.
The pickup did not have any licence plates attached to the front or back of the vehicle.
The couple first noticed the white pickup as they were travelling north along Chao Fa West Rd, Ms Kwannapa said.
The pickup pulled up alongside and the driver invited her and her husband to step out of the truck. The pickup driver reportedly held up a gun to show them his threat. The couple declined and stayed in the truck.
The same again happened when they pulled up at the traffic lights just north of the King Power outlet, Ms Kwannapa added.
By the time they had reached the Naka Intersection, her husband just wanted to keep on driving to get away from pickup driver, she said.
The truck and pickup went separate ways when the pickup entered the Darasamut Underpass and the truck stayed on the surface road.
Wichit Police Deputy Chief Pol Lt Col Wuttichai Chanfai received the complaint, and confirmed that police were now looking for the pickup and its driver.
Wichit Police Chief Pol Col Chatri Chukaew has been informed of the incident, Pol Lt Col Wuttichai noted.