The most powerful solar storm in more than two decades struck Earth on Friday, triggering spectacular celestial light shows in skies from Tasmania to Britain — and threatening possible disruptions to satellites and power grids as it persists into the weekend.

The first of several coronal mass ejections (CMEs) — expulsions of plasma and magnetic fields from the sun — came just after 1600 Greenwich Mean Time, according to the National Oceanic and Atmospheric Administration's (NOAA's) Space Weather Prediction Center.

It was later upgraded to an "extreme" geomagnetic storm — the first since the so-called Halloween Storms of October 2003 caused blackouts in Sweden and damaged power infrastructure in South Africa. More CMEs are expected to pummel the planet in the coming days.