Peter de Graaf, Northland reporter

A Northland lines company says substation break-ins are endangering lives and causing power cuts affecting thousands of people.

Top Energy chief executive Russell Shaw said he was shocked by what he described as the offenders' "astonishing recklessness" and "absolute stupidity".

In the most recent break-in, thieves took essential equipment from a substation and forced a power shutdown that left 4500 Far North homes in the dark.

Shaw said the thieves also sabotaged a high-voltage earth connection, putting themselves - and any staff working at the substation afterwards - at serious risk of electrocution.

In another break-in, thieves damaged generators and made them unusable just before Cyclone Tam storm hit.

Shaw said backup generators were vital for keeping the power on while storm damage was repaired.

He said interfering with electrical equipment could trigger widespread outages, affecting homes, businesses and essential services.

His message for would-be thieves was simple: "Don't do it. You're jeopardising your life and those of others. It's not worth it."

Shaw said the company was beefing up security at its substations across the Far North.

He said they were high-voltage facilities that could cause serious injury or death to anyone who entered without proper training and protective gear.

Networks general manager Claire Picking said Top Energy facilities had been broken into 18 times, including eight substations, so far this year.

The items taken were of relatively low value, while the risk to the thieves, staff and the public was "very high".

The removal of a substation earth connector was particularly dangerous, she said.

Shaw urged anyone who saw suspicious activity near Top Energy substations or other electricity infrastructure to call the police immediately, or the company on 0800 867 363.

Under the Crimes Act, the maximum penalty for sabotage of essential infrastructure is 10 years' imprisonment.

Top Energy would not say which substations had been targeted for fear of causing deadly copycat break-ins.

This story was originally published by RNZ