Railway barrier arms at several Christchurch crossings are out of action after a train collided with iron deliberately placed across the track.
Inspector Michael Coulter said someone had placed two pieces of railway iron across the railway track in the Christchurch suburb of Bryndwr.
A train collided withthe iron shortly after 12.30am, sending the iron crashing into a fence and a signals control box.
"Youths were seen running nearby at the time of this incident, however it is not known if they were involved," Mr Coulter said.
He said the damage meant that barrier arms were not working at the Wairakei, Blighs and Harewood Roads level crossings.
Inspector Warren Kemp said the train driver saw the pieces of railway iron and had braked before the crash.
He said someone could have been killed and police would like to hear from anyone with information about who could be responsible. He said people should phone 03 363 7400, extension 37905.
As a result of the crash, trains were travelling at low speeds between Christchurch and Belfast.
KiwiRail spokeswoman Ruth Larsen said the company "deplores" any actions that put lives at risk.
"The behaviour of these vandals is irresponsible and frankly, it is impossible to fathom the mentality of people who behave like this," Ms Larsen said.
