An investigation is underway to determine how a SEPTA passenger bus burst into flames early Friday in South Philadelphia.

Heather Redfern, a SEPTA spokeswoman, said the Broad Street Night Owl bus was on layover at Broad Street and Pattison Avenue when the fire broke out about 1:15 a.m.

No one was on the vehicles at the time, she said.

The fire was so hot it melted a utility pole, which fell on the bus, Redfern said.

Firefighters put out the blaze and the charred bus was taken to a SEPTA yard, where mechanics and investigators will seek to determine how the fire started.