The national electricity grid operator is warning of possible insufficient power generation to meet households' demand on Friday.

Transpower has issued a notice saying there was a risk that power generation and reserves would not meet demand between 7.30am-8.30am.

It said if power generators could not provide enough electricity, Transpower would manage demand to avoid a grid emergency.

"The system operator may instruct the grid owner to disconnect feeders without further notice to connected parties," it said.

MetService has forecast temperatures to plunge overnight, with Christchurch set to fall to -4 degrees Celsius.

In 2021, almost 34,000 households lost power on one of the coldest nights of the year, as insufficient supplies were arranged for the surge in demand.

An industry panel fined Transpower $150,000 for its role in the blackouts.

This story was first published by RNZ