TAIPEI, Taiwan - Undersea fiber-optic cables were damaged by a powerful earthquake off the southern tip of Taiwan, causing the largest outage of telephone and Internet service in years and demonstrating the vulnerability of the global telecommunications network.

Two residents were killed and more than 40 injured in the magnitude-6.7 tremor that hit offshore, near the southern Taiwanese town of Hengchun late Tuesday.

Up to a dozen fiber-optic cables cross the ocean floor south of Taiwan, carrying traffic between China, Japan, Korea, Southeast Asia, the U.S. and the island itself. Chunghwa Telecom Co., Taiwan's largest phone company, said the quake damaged several of them, and repairs could take two to three weeks.

Taiwan lost almost all of its telephone capacity to Japan and mainland China. Service to the United States also was hard hit, with 60 percent of capacity lost.

Later, Chunghwa said connections to the U.S., China and Canada were mostly restored, but 70 percent of the capacity to Japan was still down, along with 90 percent of the capacity to Southeast Asia.

Stephan Beckert, an analyst with the Washington-based research firm TeleGeography, said it was the largest telecommunications failure in years.

"The magnitude of the break is surprising because Taiwan is otherwise a very well connected system," Beckert said. He noted that cables get cut and disrupted all the time, but there's usually enough backup capacity on other lines to keep traffic flowing without customers noticing an interruption.

But with multiple cables broken in one blow, Internet traffic around the Pacific was disrupted. Hong Kong telephone company PCCW Ltd. (PCW), which also provides Internet service, said the quake cut its data capacity in half. Internet access was cut or severely slowed in Beijing, said an official from China Netcom, China's No. 2 phone company.

The official, who would not give his name, said the cause was thought to be the earthquake, but he had no further details.

The Internet Traffic Report Web site, which monitors Internet connectivity in several countries, showed that packet loss, or the percentage of data that doesn't reach its destination, spiked sharply in Asia at the time of the earthquake, rising from about 10 percent to more than 40 percent.

On Wednesday afternoon U.S. time, the Web site showed limited connectivity to China, Singapore and Indonesia, while Japan and Taiwan were apparently back to normal.

KDDI Corp., Japan's major carrier for international calls, said its fixed-line telephone service was affected by the quake. Company spokesman Haruhiko Maeda said customers were having trouble calling India and the Middle East, which usually use the cables near Taiwan. Maeda said the company was rerouting calls through the U.S. and Europe.

South Korea's largest telecom company, KT, said that the lines it uses were damaged, affecting dozens of companies and institutions, including South Korea's Foreign Ministry.

In the U.S., Cisco Systems Inc. (CSCO)'s Linksys unit warned that customer support call centers for its home networking gear were affected by the outage, but other companies with overseas call centers reported few problems.

Molly Faust, a spokeswoman for American Express Co., the global travel and payment card company headquartered in New York, said the company "wasn't experiencing any customer service issues in Asia."

She said that there were "some interruptions" of the company's computer systems in Taiwan, but added: "It didn't impact customers because we could use backup systems and manual processes."

Tyco International Ltd. (TYC) said it has a Taiwan-based cable-laying ship heading to the area for repairs.

"Pretty much everything south of Taiwan has been reported at fault," said Frank Cuccio, vice president of marine services at Morristown, N.J.-based Tyco Telecommunications.

Cuccio expects the ship to be in position in a few days. It then takes three to five days to repair each cable, but mudslides set off by the earthquake can complicate matters by covering the cables, making them harder to retrieve from the bottom.

Cuccio said the ruptures are more than 10,800 feet below sea level, too deep for the remote-controlled submersibles that otherwise would find the cables. Instead, the ship will drag grapnels along the bottom to find them.

The cables on the deep ocean floor are just two-thirds of an inch, a testament both to the immense data capacity of optical fiber and the fragility of the links that form the global telecommunications network.