Police say it was lucky no one was seriously injured in a rail accident after iron was placed deliberately on the tracks, causing a freight train to crash.
The train crashed into two lengths of iron which had been placed across the track near Blighs Road in Christchurch.
Significant damage was caused to a signal box beside the line and three of the city's busiest level crossings are out of order.
Neither the lights nor the barrier arms are working at the crossings on Blighs Road, Wairakei Road or Harewood Road on Friday.
Senior Constable John Hodgen says the act was "absolute mindless sabotage."
"The train driver could've been killed by the iron being flicked up, the train could have been derailed and caused damage to neighbouring houses - just absolute mindless stupidity.
"It's just typical of what we have to put up with in society nowadays."
Mr Hodgen says police want to talk to a group of skateboarders seen running from the area.
KiwiRail says it will take at least a day for the system to be fixed.
In the meantime, trains will be running at a reduced speed and motorists are advised to take extreme caution.