KEY POINTS:
Police are investigating the possibility that a gas cylinder, perhaps left on railway lines on purpose, caused yesterday's "severe" delays to thousands of Auckland rail commuters.
A city-bound train which left Papakura with 200 people on board stopped dead on the tracks, blocking the southern and eastern railway
lines for almost three hours from 7.30am.
Detective Sergeant Steve Brewer said witnesses and passengers were now crucial to the inquiry as police looked into whether the train had a mechanical failure or if an object, believed to be a "squashed" gas bottle found near the scene, was deliberately placed on the tracks.
Asked if the gas bottle could have been an act of retaliation by someone angry at this week's nationwide anti-terrorism operation, which has so far seen 17 people arrested, he said: "At the moment we've got a completely open mind. We're not ruling anything out.
"No one's claimed responsibility for the gas bottle that was found 2m from the train track and we know of no link to what's happened earlier in the week."
"Obviously if it was genuine intention that a quite large foreign object was placed on the track, that's extremely serious and that's a case of seriously endangering public safety," he said. Large metal train parts, believed to be brake callipers, broke away during the incident.
Mr Brewer said another train left Papakura at 7.19am and had no difficulty on the tracks. Eleven minutes later, the affected train stopped. Its first three carriages were not affected but the fourth was damaged in the incident.
It was possible someone had thrown an object underneath the train as it moved but police were relying on witnesses and passengers who they hoped could help solve the mystery, he said.
Nick French, general manager of Veolia, the company which runs Auckland trains, estimated between 2500 and 3000 people were affected by the disruption.
"Trains weren't able to get past the vehicle so it severely delayed all services on the southern and eastern line."
He said bus and taxi companies were called to ferry passengers to Auckland, transferring people between Papakura and Puhinui.
The disruption was made worse because it occurred in peak times, when the alternative transport options were busy, he said.
No one was injured and train services had returned to normal by 10.30am.
Any passengers who have not spoken to police and anyone who saw suspicious activity in the railway area near Papakura is asked to contact police on (09) 295 0200.