By Yereth Rosen

ANCHORAGE, Alaska (Reuters) - An overnight wind storm with gusts of over 100 miles an hour at high elevations knocked out power to at least half of Alaska's largest city in the biggest outage in Anchorage's center in decades, municipal and utility officials said on Wednesday.

"It's incredibly substantial. A huge proportion of Anchorage is affected," said Dawn Brantley, emergency program manager for the Municipality of Anchorage.

She said she did not know yet what percentage of the city overall had been affected but called the outage the biggest for downtown Anchorage in decades.

Electricity was cut to at least half of Anchorage, including nearly all customers of the utility that serves the central part of the city, the officials said.

Tens of thousands of homes and businesses remained without power by midday on Wednesday, Brantley said.

Both of Anchorage's electrical utilities, city-owned Municipal Light and Power and member-owned Chugach Electric Association, suffered outages.

Power outages caused schools, local colleges and state offices to close on Wednesday. Access to Joint Base Elemendorf-Richardson was limited to essential workers. But municipal offices were open, Brantley said.

The storm knocked down large trees and caused some property damage, but no storm-related injuries were reported, she said.

(Editing by Dan Whitcomb, Cynthia Johnston and Sandra Maler)