(CNN) All nine people aboard an aging cargo plane making its final military flight Wednesday were killed when the aircraft nosedived onto a Georgia highway.

The Puerto Rico Air National Guard WC-130 was carrying nine crew members when it crashed, the Guard said in a statement. It was flying from the coastal city of Savannah, Georgia, to Tucson, Arizona, where it was to be decommissioned.

The plane involved in Wednesday's crash was at least 50 years old, according to an official familiar with the aircraft.

"Nine crew members died in the accident, but until their families and relatives are notified, we cannot give their names," Brig. Gen. Isabelo Rivera said. "Our prayers, thoughts and condolences to the families and loved ones of our aviators."

One witness said the plane made a "loud, strange noise" just before the crash. Another said the ground shook as if a bomb went off when it hit.

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