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.