Southern California Edison reported at about 10:10 p.m. that the power had been restored pending further evaluation. Residents were asked to reset their circuit breakers if power did not work.
About 650 residents, mostly around the Civic Center, remained without power, Mayor Robert Garcia said.
"We are pleased that the vast majority of those without power, now have power," Garcia said.
Just after 2 a.m., Southern California Edison crews were trying to test underground power lines at Locust Avenue and 6th Street when smoke began seeping out of manholes.
The city of Long Beach had tweeted that the setback would affect 5,200 customers.
Power tests ran @ 2:10am. Smoke out of potholes around 6th+Locust now. Fix needed. 5,200 customers without power again in a few mins.— City of Long Beach (@LongBeachCity) July 17, 2015
An SEC spokesman said approximately 3,200 customers were without power Friday morning.
That figure is up from 2,700 customers affected on Thursday. The outage began Wednesday after an underground electrical fire near 3rd Street and Chestnut Avenue. The fire caused manhole covers in downtown Long Beach to blow off.
Area residents are frustrated and angry that things appear to be getting worse, not better.
"It's horrible. I've had to take food to my daughter's house, who lives in another city. It disrupts your life completely," said resident Richard Pancoast. "Especially at night, it's hard to get around, even in your own place."
SCE workers handed out water, ice and flashlights to residents struggling to get by without electricity.
Flashlights, ice and water available at 10:00 AM at 730 Pacific Ave in downtown #LongBeach. We will resupply until outage is over.— SCE (@SCE) July 17, 2015
Firefighters are advising residents to be very careful when using candles for lighting to avoid fires.
The outage was also impacting freeway traffic, with northbound lanes of the Long Beach (710) Freeway closed at the Third Street onramp, and southbound off ramps closed at Broadway and Sixth Street.
Congestion was also evident along surface streets across downtown Long Beach, where many traffic lights remain blacked out.
City News Service contributed to this report.