Authorities are investigating the cause of a fire that damaged a SEPTA bus near the Philadelphia International Airport Thursday morning.

The Route 68 bus was parked in the UPS Employment Center lot on Hog Island Road around 8 a.m., when its operator reported a fire in the rear right tire area, a SEPTA spokeswoman said.

Firefighters responded and extinguished the blaze, but not before it spread to the vehicle's brake line, according to the transit agency.

There were no passengers aboard the bus, which was just starting its route to Broad Street and Oregon Avenue, and no injuries were reported.

The blaze was the second reported on a SEPTA bus in recent months. In April, a Broad Street Night Owl bus burst into flames at Broad Street and Pattison Avenue.