One hundred steel railway clips used to hold tracks in place have been stolen from a rail line in the Auckland suburb of Takanini.
Manukau police say that the line was closed at the time and people working on the site noticed the missing clips and replaced them immediately.
Senior Sergeant Mark Rowbottom says a man died when he was hit by a train in Wellington last week while attempting to take metal weights from a railway track.
He says one clip is only worth 50 cents, but its removal could cause a possible train derailment or death.
Police are also concerned about copper thieves who are targeting the earth wires that are part of a safety system for power delivery, he says.