SAN DIEGO (CNS) - More than 500 customers are without power in Kearny Mesa following a transformer explosion.

Calls about a loud explosion and a downed power line began coming in at about noon Saturday, said Officer Tony Martinez of the San Diego Police Department.

Wes Jones, a spokesman for San Diego Gas and Electric, said initial reports indicated that the outage was triggered by some kind of vehicle collision, but the cause is currently unknown.

"There's some speculation that a vehicle came into contact with overhead wires, but nobody knows for sure," Jones said.

Martinez said police had not received any reports of a crash.

Power was expected to be restored by 6 p.m., Jones said.