The downed power lines were reported at 1:37 p.m., said CHP Officer Nathan Logan.
Minutes later, the CHP closed the westbound lanes at Harbor Boulevard and the eastbound lanes at Euclid Street, Logan said.
Authorities suspect a large truck may have hit something that caused a chain reaction resulting in the lines coming down, Logan said.
The accident also knocked out power to advisory signs alerting motorists to the freeway shutdown, Logan said.
Westbound motorists were being detoured to the northbound Orange 57 Freeway and eastbound drivers were being detoured to the southbound Santa Ana 5 Freeway, Logan said.