The incident happened on Mittraphap Road in Ban Haet district.
Firefighters from several government agencies took around an hour to put out the flames.
The injured passengers were taken to Sirindhorn Hospital by the hospital's medical personnel and the rescue team from Phutthayansamakhom Ban Haet Foundation.
The bodies of the three adults and two children who died were taken to Srinagarind Hospital for autopsy.
"I opened the bus doors to allow the passengers to escape, but it was too late because the flames spread quickly," said the tour bus driver.