At the bottom of the hill on the Patong side, Kathu police said a six-wheeled truck had broken down, blocking traffic.
On the Kathu side of the hill, there had also been a small crash involving at least one car. There were no reported injuries in the crash, and the car had since been moved away from the traffic.
Police told The Phuket News traffic was expected to be flowing smoothly again in around one hour.