Auckland trains are now running on a restricted basis after a signal fault brought all lines in the city to a stop this morning.
An Auckland Transport spokesman said KiwiRail operated the signals and it was working with them to fix it.
KiwiRail said the signal fault made it unsafe for the trains to move and had to halt all services.
It said a backup system failed to activate but an older back up system was now operating and allowing some trains to move on a restricted basis.
KiwiRail chief operations officer Henare Clarke said the cause of the initial fault was still being investigated and its teams were working at pace to fix the issue.
"Some trains are now moving in the city on a third, older system while a team of 25 from around the country look to fix the issue. Investigations are centring on a controlling system in Auckland," he said.
Auckland Transport said teams were working to have passengers disembark and apologised for any delay and inconvenience.
One citybound passenger, Nicola, told the trains to Britomart station usually stopped through the tunnel to allow other ones to exit but this time it stayed for much longer.
"We ended up about halfway into the tunnel at Britomart and it stopped, which isn't unusual but we ended up being stopped for an hour and then they asked us to evacuate the train and walk through the tunnel."
A commuter stuck at Takanini station, Gulnaz Merchant, said she got a notification on her phone that no trains were available.
"I am really stuck as I go to work by train. So Il have to take other options, go by a car or take a bus. Those are the only two ways to go.
"I am working so it has really disrupted my day."
Another commuter stuck at the station, Ray Kuo, said he had no notice of the delays.
"Probably going to take a bus but just checked Google maps and it shows me that it would take like two hours to arrive at the office.
"I am trying to talk to my boss to see if I can work from home today."
KiwiRail are currently investigating the Signal fault and no trains will operate until further notice. https://t.co/YZuu6A1ISO— Auckland Transport (@AklTransport) January 24, 2019
For those who are still on board services between stations, our teams are working to have passengers disembark very shortly. We apologise for the delay and inconvenience.— Auckland Transport (@AklTransport) January 24, 2019
Some train passengers are posting on social media that they've been sitting at stations for a while.
Been sitting outside Britomart for 35 minutes and we're being kept in the loop as much as possible— Idlewild Child () (@coolian2) January 24, 2019
I've been sitting on a train outside britomart for 20 minutes now. Would be nice for another update as we're not getting much from the train manager.— Robert Mcleod (@itbytesbob) January 24, 2019