The bus exploded at around 7:30 pm after the packed bus pulled into a stop, the Xinhua News Agency said, adding that the blast and flames injured people waiting for the bus.
"I heard a bang, and in five minutes, the bus was reduced to a frame," an unnamed passenger who escaped the bus was quoted as saying.
Guangzhou police said on their microblog that they were investigating the incident, which occurred in the Haizhu district of the city. They said two charred bodies had been found at the scene.
The incidents come at a time when Chinese authorities are on edge following a series of violent attacks blamed on Muslim extremists, causing them to increase security at airports and train stations, and on buses.