HONOLULU, Dec. 6 (UPI) -- Gale-force winds and driving rains pounded Hawaii, causing flash floods and leaving thousands Thursday without power.

A massive storm with winds topping 50 mph slammed into the Hawaiian islands Wednesday in what many say was some of the worst weather in recent memory, the Honolulu Advertiser reported.

"It was like a monstrous hurricane," one resident said.

Numerous schools remained closed for the second day Thursday as officials scrambled to clear debris and deal with downed power lines and telephone poles. Mail service also was disrupted.

High wind warnings remain in effect for Maui and Hawaii through Thursday evening and flash-flood watches were issued across several of the islands, the Advertiser said.

An estimated 45,000 customers lost power from the storm, though no major structural damage was reported.

Four people suffered minor injuries.