A Delta Air Lines plane undergoing maintenance testing ran off a taxiway and down an embankment at Hartsfield-Jackson International Airport early Tuesday.

Delta spokesman Eric Torbenson said mechanics were testing the engines of the Boeing 737-700 around 5 a.m. when the incident occurred. There were no passengers on the jet.

The plane ran off the end of a taxiway adjacent to Runway 26-L and over an embankment near the northeast corner of the airfield.

There were no injuries to the two mechanics on board the plane, which Torbenson said sustained "significant damage."

Delta spokesman Anthony Black said late Tuesday morning that “the cause is undetermined and under investigation.”

The plane had flown into Atlanta from southern California's John Wayne Airport Monday night, according to the FlightAware flight tracking website.

Runway 26-L was closed following the incident. At 9:30 a.m., flights were departing, but not arriving, on that runway.