The heavy collision trapped the passengers in the car. Rescuers had to use equipment to free them just as the vehicle caught fire.
Another group of rescuers quickly succeeded in extinguishing the flames, preventing further casualties.
The five injured people were taken to hospital. The accident also created a traffic jam.
Pickup driver Jetsada Norakaipan, 29, admitted to falling asleep and causing the accident.
The police are investigating to find out exactly how the crash occurred.
San Kamphaeng police station is holding the vehicles until the injured retrieve them.