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A public bus has exploded into a ball of fire in the heart of Rome's historic center after an apparent electrical short circuit. No one was seriously injured.

Dozens of tourists and passersby watched in awe as the flames engulfed the bus, shortly after 10 a.m. Tuesday. Several explosions popped, setting off nearby car alarms.

The blaze charred several stories of the nearby building along the Italian capital's Via del Tritone, just a few blocks from the premier's office and the Trevi Fountain.

Prosecutors and the public transport service ATAC opened investigations into the cause. The ANSA news agency said it was apparently sparked by a short circuit.