A high-speed train traveling from the southeastern port city of Busan stopped abruptly inside a tunnel on its way to Seoul on Sunday, the latest incident in a series of technical problems for the bullet train, its operator said. The KTX train remained stationary for about an hour from around 11 a.m. inside Hwangak Tunnel in Gimcheon, about 234 kilometers southeast of Seoul, before resuming service, Korea Railroad Corp. (KORAIL) said.