Firefighters are trying to figure out the cause of an early morning fire at the Sonic Drive-In, 10603 Burbank Drive.

Firefighters from the St. George Fire Department were called to the scene just after 5 a.m., St. George Fire Department spokesman Eldon Ledoux said.

The fire was contained to the front corner of the building and the drive-thru but there was smoke damage throughout the restaurant, Ledoux said.

The restaurant was not open and no one was injured.

The cause is undetermined and under investigation, Ledoux said.