KOMO/ABC News

A commuter bus burst into flames on Interstate 5 in Seattle during the heart of the morning commute today, but the fire department said the driver's quick thinking helped prevent deaths or injuries.

"The bus driver said he heard a couple of pops and evacuated 30-40 people off the bus," fire department spokesman Kyle Moore told ABC News. "He not only evacuated them but moved them a significant distance away, which helped greatly with our firefighting efforts."

"Everyone starts looking around at each other, like, 'Whats happening?'" passenger Emalasa Franulovich told ABC affiliate KOMO-TV. "Then we hear a second 'pop' and everyone starts panicking and yelling, 'Get off the bus."

The fire erupted before the bus came to a full stop, and soon consumed its rear half.

Aerial footage of the blaze showed billowing clouds of black smoke from the bus and traffic backed up for miles. Firefighters were able to extinguish the fire around 7:30 a.m. local time.

Moore said that the blaze could have been much worse had the bus been powered by natural gas, and not by diesel fuel. "Diesel fuel is not explosive like a natural gas bus," he said.

Police and Sound Transit, which owns the bus, are investigating the incident.