Thousands of homes and businesses in Nogales are without electricity after a power surge caused by an apparent arc fire in one of the city's generators.
Nogales police say the power surge occurred late Wednesday morning at the Valencia substation of UniSource Energy Services.
UniSource officials say they have identified the problem and are making repairs, but power could remain out for several more hours.
Nogales police say no injuries have been reported and foul play isn't suspected in the power failure.
A spokesman for UniSource says the cause of the outage is being investigated.
All of the city's major traffic lights were affected, though some have come back online.
Nogales police and fire departments are working together to make sure traffic is moving.