An explosion at a power plant in Nogales left about 10,000 local residents without electricity for more than two hours Wednesday afternoon. A Nogales Fire Department crew was in the vicinity of the UniSource Energy Services facility on North Grand Avenue and West White Park Drive when the power went out, said NFD Chief Mike McKearney. "They witnessed a large explosion with an ensuing fireball and large plume of smoke," McKearney said. Nogales firefighters evacuated a nearby business as a precaution and let smaller, secondary fires burn out, he said. No injuries were reported, he said. Nogales police spokesman Sgt. Robert Fierros said in a tweet that no foul play was suspected in the power failure. The cause of the outage is still being investigated, said UniSource spokesman Joseph Barrios. The UniSource Energy Services outage map showed most of Nogales and eastern Santa Cruz County was without power from just before noon to about 2:30 p.m.