A bus driver changing a tyre has escaped unhurt after the vehicle burst into flames.

The 45-seat kaBOOM party bus was on its way to collect schoolchildren for an excursion when a tyre burst, near Mallala on Adelaide's northern outskirts.

The driver managed to pull over safely and was attempting to change the tyre when fire erupted.

Country Fire Service crews took half an hour to put out the blaze, which destroyed the bus which had a KABOOM1 numberplate.

Max Wooldridge was driving by and stopped to help.

"We didn't know it was on fire until we went to go change it (tyre) and then we noticed there was some flames so we ran inside the cab to get the extinguisher," he said.

"Came back, doused it with the whole extinguisher and just wasn't enough.

"It was just much too hot and it spread much too far."

No-one was injured during the emergency.