'Too early to say': Investigators on cause of Wellington train derailment

Investigators say it is "too early" to determine the cause of last night's derailment of a Wellington passenger train that caused major damage and left six people injured.

The Transport Accident Investigation Commission (TAIC) said it had appointed an investigation team after a Metlink train came off the tracks between Khandallah and Box Hill stations on the Johnsonville Line at around 7.20pm.

The train had been running a southbound service from Johnsonville to Wellington.

Wellington Free Ambulance responded with six units and transported six people to Wellington City Hospital. A spokesperson said two had serious injuries and four had minor injuries.

Investigation after Wellington train comes off rails, passengers hospitalised - Watch on TVNZ+

Eight people were initially reported to have been injured – this was later corrected.

Metlink said rail services on the Johnsonville Line would be closed and replaced with buses until Thursday. On average, around 3000 passengers use the service on an average weekday.

"Bus replacement services will operate to a Sunday timetable from Monday 8 June to the end of Wednesday 10 June."

'Pretty scary' - witness

Khandallah resident Sally Wills, whose home backs onto the station platform, described the moment of impact.

"We heard a big crash and the house sort of shook a little bit — it was a bit scary. We thought at first it might have been lightning because there was some rain at the time," she told 1News.

Her husband went outside to investigate and came running back in: "There's been a train crash."

Wills said the couple grabbed coats and torches and went to help.

"He was one of the first few — a few of our neighbours had popped out to have a look, make sure people were okay," she said.

She saw one or two passengers come off the train, "stumbling — no one seemed seriously hurt" among those she saw.

"It was a pretty scary thing to hear in the middle of your Saturday evening. Very loud. Very full on."

Train collided with concrete block - KiwiRail

KiwiRail chief metro officer David Gordon said the train had come to rest against a concrete block designed to stop it running further onto the single-track section. While it remained upright, its wheels were off the tracks.

"You're going from travelling at a reasonable pace out of the station, it's not full noise, but at a reasonable pace, into a solid stop."

He said his thoughts went out to those hurt, including the driver who had hit his head and had been taken to hospital.

"This is dramatic," he said at the scene. "You get a text like this coming through... which says 'derailment and passengers injured' - it's pretty gut-wrenching.

"It's just not what you want and for the people on board, it's been worse."

TAIC chief accidents investigator Louise Cook said her team had been on site throughout the night.

"At this stage, it's too early to determine the cause of this accident. We're examining all relevant factors," she said, adding that investigators would look at the people involved, the systems, train data, and CCTV footage.

Cook appealed for witnesses to come forward. "Getting information is vital, so we're keen to hear as soon as possible from people who were on the train or who saw the accident occur. We're especially interested in receiving photos or videos."

On timeline, she said gathering on-site evidence would likely take a couple of days, but interviews, documentation and data analysis meant a full rail investigation typically takes 12 months to two years.

Greater Wellington Regional Council chairperson Daran Ponter said a contingent of staff from KiwiRail, Transdev and Rotem were on site.

Minister for Rail Winston Peters said the incident was "concerning" and that his thoughts were with those on board.

"The network is designed with multiple layers of safety. If a train passes a red signal at Khandallah, it is diverted to a runoff line to prevent any risk of collision with another train," he said.

"The carriages also appear to have responded as designed — while the images are alarming, two critical safety systems appear to have functioned as intended."

Johnsonville Line services have been replaced by buses until further notice. Before the derailment, buses were already set to replace trains until 6pm for routine works.

Fire and Emergency NZ crews from Johnsonville and Porirua helped remove all passengers from the train.

Metlink senior operations manager Paul Tawharu said the cause of the derailment was unknown.

"My immediate thoughts are for the safety and well-being of the passengers and Metlink staff on board," he said in a statement to 1News.

The Johnsonville Line is a 10km single-track commuter rail line running between Wellington's central station and Johnsonville through the city's northern suburbs.

The line passes through seven tunnels and steep terrain, climbing more than 150m above sea level, with a maximum speed of 60km/h.