Police inspector Danielle Peres said the crash occurred Wednesday morning when the driver lost control of the bus on a rain-soaked road in the Rio de Janeiro district of Sao Goncalo.
She said the vehicle then hit the light post, loosening a power transformer that then fell on the bus and exploded, "causing the fire that destroyed the vehicle."
Another nine people who survived the crash were rushed to nearby hospitals with non-life-threatening injuries, she said. Peres said police were trying to determine if the bus driver was speeding when the accident occurred.
"But unfortunately most of the other passengers were unable to get out of the bus. The heat inside was very intense," he said.
Wilian Lemos, one of the injured passengers, told O Globo he was sitting at the rear of the bus and managed to escape by jumping out a window with the help of the men at the gasoline station.