Capt Kornphoomphot Pongpaiboon of the Thalang Police said officers were informed of the accident, in Moo 9, Thepkrasattri, at 1:49pm.
Police along with rescue workers from Pa Khlok Municipality and Phuket Kusoldharm Foundation arrived at the scene to find a grey Ford Ranger pickup truck with heavy damage to its front.
At the side of the road were two motorbikes with sidecars (saleng). One had been destroyed by the impact.
The driver of one of the saleng, Somyot Sawasdee, 55, a resident of Moo 9, Pa Klok, was dead at the scene
The driver of the other saleng, Anuwat Aramrakseri, had suffered critical injuries. Mr Anuwat was rushed to Thalang Hospital, but later pronounced dead.
The driver of the Ford Ranger pickup, Thotsawan Bunyanit, 33, a resident of Phuket Town, told police he was driving from Baan Muang Mai to Pa Klok when the accident happened.
He was heading downhill when he realised that two saleng were driving toward him side by side on his side of the road.
It appeared that one of the saleng was trying to overtake the other while both were driving up the hill on the wrong side of the road, Mr Thotsawan said.
By the time he realised what was happening he was unable to avoid the collision, Mr Thotsawan added.
Police seized all three vehicles as evidence.
Officers are continuing their investigation, and noted that they will review the dashcam footage from the Ford Ranger before proceeding with any legal action.