HONOLULU -- Hawaiian Electric Co. crews restored power to at least 5,500 customers in Pearl City and Waipahu Wednesday morning.

A spokesman for HECO said the company is investigating the cause of the outage, KITV reported.

St. Joseph School in Waipahu is closed Wednesday because of the outage. A spokeswoman with the Hawaii State Department of Education said all public schools are open.

More than 2,500 residents from Nanakuli to Lualualei had no electricity for an hour earlier, but power was restored at 4:30 a.m., according to HECO.