Police say a 36-year-old man has been arrested in connection to a series of thefts of materials along the rail line between Featherston and Greytown this year.

Detective Senior Sergeant Philip Skoglund said the man's alleged offending had caused "extensive damage" to the rail network.

"The offending is alleged to have primarily targeted sections of the rail line between Featherston and Greytown. Specifically, signalling power cabling within the rail corridor was stolen, causing significant disruption, extensive damage, and considerable repair costs to KiwiRail infrastructure," Skoglund said.

He said police enquiries into the full extent of the thefts were ongoing and he urged members of the public who had seen any suspicious activity or vehicles on the Wairarapa railway line to contact police.

In June Wellington Metro general manager Andy Lyon told RNZ nearly 5km of cable had gone missing from rail infrastructure in the Wairarapa in the first six months of the year.

"While the scrap cost is very low, the cost to replace these cables runs into the hundreds of thousands of dollars," Lyon said.

On Friday Lyon warned that people interfering with rail equipment were putting themselves and others at risk of "serious harm".

"In this case, the theft involved copper cabling associated with our signalling system, which is preparing the network for Greater Wellington's new trains. As well as posing a significant safety risk, this type of offending can cause delays, additional costs and disruption to the community," Lyon said.

Lyon said KiwiRail was grateful for the swift actions of police and would continue to work closely with them to combat similar offending.