At least seven firefighters have been injured in an explosion that left three in critical condition in Southern Los Angeles on Thursday morning.

Just before 7 a.m., the Los Angeles Fire Department (LAFD), responded to a call about a truck with pressurized cylinders on fire in Wilmington, a neighborhood in the South Bay and Harbor region of LA.

An explosion ensued, injuring an estimated seven firefighters total, according to an LAFD alert. Three were transported to the hospital immediately, with at least two of those injured listed in critical condition.

The rest of the injured were evaluated at the scene while awaiting further ambulance response. The initial cause of the fire and the circumstances of the explosion are still not known.