An unusually strong solar storm hitting Earth has produced stunning displays of colour in the skies across the world.

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

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

There were also spectacular displays in the Southern Hemisphere, with widespread reports from Australia and New Zealand.

The US authority 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 the administration’s Space Weather Prediction Centre.

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The storm could produce northern lights as far south in the US as Alabama and Northern California, the administration 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 could come from phone cameras, which were better at capturing light than the naked eye.

Snap a picture of the sky and “there might be actually a nice little treat there for you”, said Mike Bettwy, operations chief for the prediction centre.

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, administration space weather forecaster Shawn Dahl said.

The storm poses a risk for high-voltage transmission lines for power grids, not the electrical lines ordinarily found in people’s homes, Dahl said.

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Satellites also could be affected, which in turn could disrupt navigation and communication services on earth.

An extreme geomagnetic storm in 2003, for example, took out power in Sweden and damaged power transformers in South Africa.

Even when the storm is over, signals between GPS satellites and ground receivers could be scrambled or lost, according to the administration.

But there are so many navigation satellites that any outages should not last long, Steenburgh said.

The sun has produced strong solar flares since Wednesday, resulting in at least seven outbursts of plasma.

Each eruption, known as a coronal mass ejection, can contain billions of tons of plasma and magnetic field from the sun’s outer atmosphere, or corona.

The flares seem to be associated with a sunspot that’s 16 times the diameter of earth, the administration said.

It is all part of the solar activity ramping up as the sun approaches the peak of its 11-year cycle.

NASA said the storm posed no serious threat to the seven astronauts aboard the International Space Station.

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The biggest concern was the increased radiation levels, and the crew could move to a better-shielded part of the station if necessary, according to Steenburgh.

Increased radiation also could threaten some of NASA’s science satellites.

Extremely sensitive instruments would be turned off, if necessary, to avoid damage, said Antti Pulkkinen, director of the space agency’s helio-physics science division.

Several sun-focused spacecraft are monitoring all the action.

“This is exactly the kinds of things we want to observe,” Pulkkinen said.

Musk’s satellites disrupted

The situation was putting pressure on Elon Musk’s Starlink satellite system, the billionaire entrepreneur said.

Starlink, the satellite arm of Musk’s SpaceX, warned of a “degraded service” as the earth was battered by the biggest geomagnetic storm due to solar activity in two decades.

Starlink owns about 60 per cent of the roughly 7500 satellites orbiting earth and is a dominant player in satellite internet.

The thousands of Starlink satellites in low-earth orbit use inter-satellite laser links to pass data between one another in space at the speed of light, allowing the network to offer internet coverage around the world.

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-AAP