One of China’s most used rockets, the Long March 7A, exploded a little more than a minute after lifting off on Monday evening, local time.

The medium-lift rocket’s payload was classified, but it was believed to be a military communications satellite. The rocket’s liftoff from Wenchang Space Launch Site appeared to be nominal, but publicly captured videos (such as this one) showed that the rocket’s first stage exploded about 1 minute and 20 seconds into flight.

The Long March 7A rocket was developed by the China Aerospace Science and Technology Corporation and is operated by the state’s space agency. As of Monday night in China, state officials have not commented on the explosion.

Was it an engine issue?

Based on the timing of the explosion, it occurred during the flight of the first stage of the vehicle, likely around the time of maximum dynamic pressure as the rocket accelerated through the lower atmosphere. It’s possible that the vehicle’s flight was ended by on-board ordnance known as a “flight termination system,” which ignites when the vehicle veers off course.

China’s state-operated launch industry has had considerable success in the last half-decade as it has grown its annual launch total to 50 or more flights per year. During that time, it has only suffered a handful of launch failures.

Due to the uncertainty surrounding the cause of Monday’s failure, the significance of the problem is difficult to ascertain. Given the closed nature of China’s state-operated space program, it may never be clear what caused the rocket to explode.