Photo: RNZ / Cole Eastham-Farrelly
An unplanned power outage is affecting around 3500 households in the Tekapo and Albury area.
Transpower said a crop-dusting helicopter on private land near Cave severed two of conductors around 10.25am on Monday.
The pilot is safe, and was able to land and report the incident to Transpower.
The lines fell on private land, and Transpower understands no one was hurt.
Transpower executive general manager of grid delivery Mark Ryall estimated power would be restored on Tuesday afternoon.
"The crews are on site now, they've got all the materials we need, and they'll work as long as light allows this evening, and then back first thing in the morning," he told RNZ.
Local distributor Alpine Energy were looking at getting some people through the night with embedded generation, Ryall added.
He said any compensation had not yet been considered.
"The focus today is just getting the crews and the equipment there so we can repair the damage from the helicopter crash."