A coal train derailment near Otira has damaged rail infrastructure and disrupted passenger and freight services on the Midland Line.

The last wagon of KiwiRail train 834 derailed while approaching the Otira Tunnel about 10pm on Tuesday, before the train came to a stop inside the tunnel.

The loaded coal train was heading towards Christchurch. No injuries were reported.

KiwiRail General Manager Engineering and Asset Management Lynne Morton said teams were assessing the extent of the damage and what repairs would be needed.

“We are working to restore the line as quickly and safely as possible.”

Wednesday’s TranzAlpine service was restricted to Arthur’s Pass, with the return journey scheduled to depart from there later in the afternoon.

Morton said passengers should expect further disruption.

“TranzAlpine services are likely to be affected for the next few days. Affected passengers will be contacted directly and offered rebooking or refund options. Replacement buses will be arranged where possible.”

KiwiRail was also working with affected freight customers.

The Transport Accident Investigation Commission has opened an inquiry, with investigators expected to spend two to three days examining the scene.

Chief Investigator of Accidents Louise Cook said gathering evidence was the immediate priority.

“That includes examining and mapping the train and the scene, and speaking with people who witnessed the accident or were involved.”

The investigation will include an examination of the locomotive, wagons, rail infrastructure, maintenance records and operational data.

Investigators will also interview train crew and other KiwiRail staff to determine what happened and identify any wider safety issues.

The cause of the derailment remains unknown, and no date has been confirmed for the line to fully reopen.