Mobile phone service for Vodafone, Spark and 2degrees customers in Auckland has been badly affected by today's power outage.

About 160 cell sites are in the affected region and all were running on battery back-up, which was now running out.

The Vodafone mobile network had about 90 cell sites within the affected area that had no power.

The sites required power to provide mobile coverage.

There was no way of telling how many customers were affected.

As sites have their power restored, generators from those towers would be transferred to sites without generator back-up.