Listen to Styx Radio on iHeartRadioListen to Foreigner Radio on iHeartRadio

(TMZ) - Two tour buses for a Styx and Foreigner concert turned into vehicular torches early Wednesday afternoon in Philly ... TMZ has learned. 

It's unclear how the fire started, but TMZ reports one bus went up in flames ... and the fire spread to the second vehicle. 

The buses were parked and NOT occupied when they caught fire. According to TMZ, the buses are "crew buses" and not "band buses." 

The bands are scheduled to perform together Thursday in New Jersey.  

To remind you of Styx's greatness, their hits including "Babe," "Renegade," "Mr. Roboto" and "Come Sail Away."

As for the concert, the show presumably will go on.

Photo: Getty Images