Fire crews attended the scene and all passengers were able to be evacuated safely.
It is understood the bus was heading towards Perth High School when the fire started.
The road near Errol junction remained in both directions due to the bus fire following the last update from Traffic Scotland just after 12:15pm.
Traffic was also being held and stationary on approach with smoke blowing across the carriageway.
A video from the scene showed large flames and smoke billowing from the vehicle.
Another clip from a passer by showed the hollow shell of a bus following the blaze.
A Scottish Fire and Rescue Service spokesperson said: “We were alerted at 8:19am on Thursday, March 24 to reports of a double decker bus on fire on the westbound carriageway of the A90 near Errol junction.
“Operations control immediately mobilised three fire engines to the location and firefighters wearing breathing apparatus are extinguishing the fire.
“There are no reports of any casualties.
“Crews will remain at the scene until the area is made safe.”
A spokesperson for Stagecoach East Scotland said: “We can confirm one of our vehicles operating a contract on behalf of Perth and Kinross Council has been involved in an incident on the A90 this morning.
“There are no reported injuries and all passengers were safely evacuated from the vehicle.
“Passengers are being transferred to an alternative service to get to their destination.
“Safety is our number one priority and we will be assisting the investigation into the circumstances involved.”
Those on the bus were taken to a nearby golf centre.
Angus Forbes, a councillor for the Carse of Gowrie, told The Courier, said: “Thankfully all children were evacuated to safety in the local golf centre and I want to thank the driver for making sure that happened, as well as the owners of the golf centre for providing safety for the children.”