National grid operator Transpower is warning of possible disruptions to Northland's electricity supply as it shifts high-voltage lines to bypass a major slip.

A big slip just south of Wellsford is threatening two towers carrying the lines, and there is a risk more bad weather might cause further movement and bring down both lines.

Transpower general manager for grid delivery Mark Ryall said temporary towers will be set up to bypass the slip, and it has taken one line out of service to reduce the risk.

"With more rain forecast, we have removed the 110kV line from service and will lower it to the ground as a precaution," he said on Thursday.

"This will mitigate the risk of both transmission lines being affected at the same time if there are further slips."

Northland will be reliant on the single 220kV line while the relocation is carried out, and households should take precautions such as having barbecues ready, and making sure electronic devices are charged.

"We are conscious that the people in these regions have been through a lot in recent weeks," Ryall said.

"While the risk of a fault or further slip on the 220kV line is small, we wanted to ensure that people are aware of the risk and able to take steps to prepare for any unplanned outages.

"We are working closely with local lines companies Northpower, Top Energy and Vector to manage any local impact in their areas."

The first stage of the bypass is expected to be completed by next week, Ryall said, allowing the 110kV line to be reactivated.