The electrical fire also affected KOMO television, KOMO Newsradio, STAR 101.5 FM and KVI, which broadcast from the building.
The small electrical fire broke out around 11 p.m. Thursday in the basement of Fisher Plaza at an electrical vault — the section of the building where city power lines meet the building's transformers, said Seattle City Light spokesman Scott Thomsen.
Subsequent power failures affected operations for many Web sites and services.
Among those affected was Authorize.net Holdings Inc., based in Marlborough, Mass. The company provides credit card services for more than 238,000 merchants. Authorize.net's Web site was down Friday morning. However, the company is saying on its Twitter account that most of its services are back online. Calls to Authorize.net's spokesman were not immediately returned Friday morning.
The travel section of Microsoft Corp.'s new search engine — Bing — was also disrupted. In a Web post on Bing.com, Microsoft said Bing Travel servers were knocked out because of the electrical problem.
"This is isolated to Bing Travel only, and there has been no impact to any other aspects of Bing. We're hard at work to restore service following this unexpected event and appreciate your patience," the posting said.
How many Web sites experienced problems was not immediately clear.
Rob Dunlop, vice president of operations for Fisher Communications Inc., said one of the main clients who uses the data center is Internap Network Services Corp., a company that manages data centers and routes Internet traffic. Calls to Internap were no immediately returned Friday.
The electrical problem forced the evacuation of the building and disrupted the late night newscast, Dunlop said.
KOMO Newsradio and KOMO-TV are broadcasting Friday from remote locations.
Our radio staff is broadcasting from our transmitter sites, and KOMO 4 News broadcasted its evening shows from a deck at Fisher Plaza.
Fisher Communications released a statement saying Fisher engineers are working with Seattle City Light and the company that manages the Fisher Plaza building to restore power and determine the cause of the electrical problem.
The Associated Press contributed to this report.