A high-speed KTX train bound for Seoul from the southern port city of Busan temporarily halted near a tunnel south of the capital on Friday due to a heat sensor malfunction caused by unknown reasons, officials said.

The incident forced Seoul-bound KTX lanes to shut down for more than 40 minutes, starting at 8:24 a.m.

Korea Railroad Corp. (KORAIL) said electric sensors malfunctioned and the captain halted the train for safety checks.

"The sensors are attached to every car. The captain stopped the train as a sensor detected heat," said an official from KORAIL. "It's not an engine failure."

KORAIL said it will look into the reasons for the malfunction of the sensor, dealing with mounting security concerns over the high-speed train.

 Another KTX train derailed while on its way to Seoul from Busan on Feb. 11, caused by a combination of mistakes, including the loss of a nut in an electronic box that controls track movement for trains. (Yonhap News)