Officials say the engine compartment aboard the bus suddenly exploded into flames at around 6 p.m. It happened near the waterfront on Broadway and Front streets.
All the tourists onboard at the time got off safely along with the bus driver.
Witnesses said they heard a loud boom and then saw flames shooting out of the back half of the bus.
The fire department managed to put the flames out quickly.
The cause of the fire is still under investigation.