Pol Lt Col Udom Phetcharat of the Phuket City Police was notified of the accident at 4:15am.
Officers and rescue workers from the Kusoldharm Foundation arrived to find the car, a red Phuket-registered Mazda CX3, crushed in the southbound entrance to the tunnel.
About 50 metres ahead was the 22-wheeled truck and trailer, registered in Phetchaburi, stopped in the right lane. The truck had damage to the right front bumper, the right front wheel and the right rear wheel had burst tyres.
Police said that both the truck and the car had entered the tunnel from the bypass road. The truck was traveling in the left lane and the Mazda car was in the right lane.
The woman lost control of the car, which collided into the truck then spun and hit the barrier, then went under the trailer and was crushed by the back wheels.
The female driver of the car somehow escaped with only minor injuries. She had been taken to hospital by relatives before the officers arrived.
The driver of the truck, Phonchai Menkaew, 39, told police that he was hauling vegetable oil from Bang Sawan in Surat Thani Province, and was on his way to deliver the vegetable oil to a depot at Ao Makham.
While driving in the left lane in the tunnel, he suddenly found that the driver of the sedan on the right side seemed to have fallen asleep and lost control. He braked as hard as he could but could not avoid being involved in the accident, he said.
The truck and car were cleared from the tunnel before the main traffic congestion began this morning.
Police are continuing their investigation of the accident, and will test both drivers for alcohol, officers said.