An express train that fatally derailed in Taiwan on Sunday had its automatic train protection (ATP) system turned off before the accident, the railway authority said Wednesday.

The Puyuma Express No. 6432 bound for Taitung from Shulin, with 366 passengers on board, derailed Sunday afternoon in Yilan, leaving 18 dead and 190 injured. It was Taiwan's worst train accident in over three decades.

A preliminary investigation showed the train was going over its set speed limit at the time of the accident. An ATP system was supposed to continually check the speed of the train and prevent it from speeding.

The island's railway authority told a press conference on Wednesday that human error was involved. The driver, surnamed Yu, switched off the ATP system but did not report it as he should have, a railway official said.

However, local media and the public have questioned whether the driver alone should be blamed and issues remain unsolved. Previous media reports said there was a problem in the signaling system of the train's control and management system before it departed, and that an anomaly was detected at Yilan Station, 18 km north of Xinma Station where the train derailed.

The result of the investigation is expected next Monday.

The railway authority has been carrying out full safety checks into its Puyuma express trains and related infrastructure, which they say will be completed in a week.

By Wednesday, normal train services on the affected railway line had resumed.