UPDATE: Quake knocks out telecommmunications across Asia.
Two cables were damaged, both off Taiwan's coast, Chunghwa said.
The company reported a 50 percent loss of overall telephone capacity, with connections to China, Japan and Southeast Asia most affected.
Chunghwa also said almost all of Taiwan's communications capacity with Malaysia, Singapore, Thailand and Hong Kong was disrupted. Also hard hit was telephone service to the U.S., where 60 percent of capacity was lost, the company said.
Internet access in Beijing was cut or extremely slow, while Japanese customers were having trouble calling India and the Middle East. In South Korea, dozens of companies and institutions were affected, including the country's Foreign Ministry.
Hong Kong telephone company PCCW Ltd., which also provides Internet service, said the quake cut its data capacity in half. Many Internet users were unable to access Web sites in parts of America, Taiwan and South Korea. Calls to Taiwan weren't connecting.