KEY POINTS:
Thousands of Auckland commuters were disrupted this morning when a train bound for the central city hit an object on railway lines.
Initial reports suggested that a gas bottle had been deliberately placed on the tracks but that has not been confirmed by police investigating the incident, which happened north of Papakura at 7.30am.
Ontrack, which runs the railway lines, blamed vandalism. A spokeswoman said people should realise they could cause a "very serious incident".
The Fire Service said there were reports of sulphuric acid at the scene.
Nick French, general manager of Veolia, the company which runs Auckland trains, estimated more than 3000 people were affected by the disruption.
All train services on the southern and eastern lines were affected because no one could pass the stopped train.
Mr French said the company was earlier calling around all bus and taxi companies to ferry passengers to Auckland.
The disruption was "severe" because the train struck the object in peak times, when most other transport options were busy, he said.
The train which hit the object had left from Pukekohe with about 200 people on board. No one was injured but parts of the train's undercarriage broke away and landed on the track. Some train services had resumed by 9.30am.
Mr French said: "Services were back up and running at 10.15am but the network will be affected for some time as there is difficulty getting replacement vehicles and staff there so there will still be severe delays."
Fire Service northern communications centre shift manager Jaron Phillips said fire crews were called at 9.30am and were still attending.
"We've had reports that there is a sulphuric acid spill which was affecting the railway and the underlying Subway Rd," he said.
- with NEWSTALK ZB, NZPA
