The US National Oceanic and Atmospheric Administration issued a rare severe geomagnetic storm warning when a solar outburst reached Earth on Friday afternoon, hours sooner than anticipated.

The effects of the northern lights, which were on display in the United Kingdom, were due to last through the weekend and possibly into next week.

Many in the UK shared phone snaps of the lights on social media early Saturday, with the phenomenon seen as far south as London and southern England.

There were sightings “from top to tail across the country,” said Chris Snell, a meteorologist at the Met Office, the British weather agency. He added that the office received photos and information from other European locations including Prague and Barcelona.

NOAA alerted operators of power plants and spacecraft in orbit, as well as the Federal Emergency Management Agency, to take precautions.

“For most people here on planet Earth, they won’t have to do anything,” said Rob Steenburgh, a scientist with NOAA’s Space Weather Prediction Center.

The storm could produce northern lights as far south in the US as Alabama and northern California, NOAA said. But it was hard to predict and experts stressed it would not be the dramatic curtains of colour normally associated with the northern lights, but more like splashes of greenish hues.

“That’s really the gift from space weather: the aurora,” Steenburgh said. He and his colleagues said the best aurora views may come from phone cameras, which are better at capturing light than the naked eye.

The most intense solar storm in recorded history, in 1859, prompted auroras in Central America and possibly even Hawaii. “We are not anticipating that” but it could come close, NOAA space weather forecaster Shawn Dahl said.

This storm poses a risk for high-voltage transmission lines for power grids, not the electrical lines ordinarily found in people’s homes, Dahl told reporters. Satellites also could be affected, which in turn could disrupt navigation and communication services here on Earth.