Transpower is disconnecting some power assets in response to an extreme solar storm.

The grid emergency now affects transmission throughout the country.

An "extreme" geomagnetic storm is affecting Earth at present.

The storm has the potential to disrupt power and satellites, as well as communications and GPS.

It is the result of a large coronal mass ejection flinging electro-magnetically charged plasma from the Sun across the solar system.

The US Space Weather Prediction Centre says G5 (extreme) geomagnetic storms can impact power grids, satellites, and radio communications.

The solar storm is expected to peak tonight, with the US Space Weather Prediction Centre forecasting severe conditions from 6-9pm (NZ time) on Saturday.

NIWA says although most solar events do not cause much impact, this is an "unusually strong event" so it pays to be prepared.

It recommends people ensure they have charged batteries and flashlights in case the power goes out.

Earlier on Saturday, Transpower said it was taking action to prevent power cuts as the strong solar storm affected the planet.

It said it did not expect power supplies to be affected.

It's the first time in 19 years that the US National Oceanic and Atmospheric Administration has issued a severe solar storm warning.