The earthquake cut cable lines under the sea and disrupted communications services for local foreign companies, the KT said.

"We have to consult with other international companies to put the disconnected lines back to normal," a KT spokesman said. "We are still in contact with them but we cannot say exactly when the service will be normalized since the fear of aftershocks remains."

According to the South Korea's Yonhap News Agency, Citigroup, HSBC, Reuters, Bloomberg and some other foreign companies operating here were affected by the disconnection, while the Foreign Ministry is also affected by the communications disruption.

The Citygroup's Internet banking service between its branches has been normalized but the service with other banks remains paralyzed, Yonhap said.