Transpower has asked North Islanders to lower power usage this morning

Transpower says there is a power emergency in the North Island and has issued a second warning notice.

The grid emergency notice warned there was a risk of insufficient generation to meet demand in the North Island.

The operator asked for more offers of power from generators and for local lines companies to manage demand as necessary.

It said it may be forced to order lines companies to shed load to avoid disconnections.

The warning covered the period from 7.15am to 9.30am.

Earlier, Transpower issued a warning notice at 5.37am that there was a risk of insufficient generation and reserve offers to meet demand in the North Island. It had asked for more offers of power and moves to decrease demand if necessary.

The emergency notice came after a sudden cold snap moved up the country in recent days.

The cold snap was lingering early on Friday with below-zero temperatures in Rotorua, which was on -3C, and Hamilton (-2C) while in the south Blenheim and Queenstown were on -1C at about 6.30am.

On Tuesday the operator said the Antarctic blast this week could set an October record for electricity demand, and though it expected the lights to stay on it would issue a notice requesting extra generation if needed.

Transpower has said it had made changes since it was held responsible by the electricity watchdog for widespread outages on one of the coldest nights of last year.