WATERTOWN, S.D.(KWAT)–Watertown Fire Rescue was called to Watertown Regional Airport Thursday morning on a report of an explosion.

The call came from an airport employee who said a fuel tank was damaged while it was being filled with fuel from a delivery truck.

Crews arrived to find the 10,000 gallon tank at the fuel farm at the airport with considerable damage.

Witnesses said while the tank was being filled, there was a small explosion followed by a plume of smoke coming from the top of the tank, near the tank vent.

After confirming there were no fuel vapors in the area, and no physical leaks coming from the tank, the entry team was able to disconnect the fill hoses and equipment connected to the fuel trailer.

The product being loaded into the fuel storage tank was 100 octane low lead fuel, which is the most common type of gas used in general aviation.

Approximately 500 gallons of fuel was loaded into the tank prior to the incident.

The cause of the incident is still under investigation. There were no injuries.