A powerful solar storm could bring a dazzling Northern Lights display later - as well as potentially disrupting GPS, communication systems and power grids.
The British Geological Survey (BGS) upgraded its forecast to the maximum and said the ongoing storm had already interfered with communications and satellite navigation.
It said a second geomagnetic "cannibal storm", feeding off the first, could reach the UK by early afternoon and be one of the biggest in 20 years.
A solar storm is an explosion of particles, energy, magnetic fields, and material blasted into space by the sun - and can disturb the Earth's magnetic field, according to NASA.
The latest event has already created the biggest geoelectric field at ground level since BGS records began.
The storm led to impressive sightings of the aurora borealis in some parts of the UK overnight and the same could happen later - assuming clear, dark skies.
People in Scotland, northern England and Northern Ireland have the best chance of seeing the lights, according to the BGS.
Cloud is forecast in other areas but the Met Office said it might break enough to provide a glimpse over southeast England.
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The colours of the aurora are produced by charged particles from the sun hitting atoms and molecules in Earth's upper atmosphere.
Solar storms can reach Earth from the sun in as little as 17 hours, but can sometimes take much longer.
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The latest one could hit the highest level of G5, according to the BGS, a rating that warns of possible power blackouts, GPS problems lasting days, and problems orientating spacecraft.
NASA says solar storms don't cause direct harm to humans as the planet's magnetic field and atmosphere protect us from the worst of the effects.
(c) Sky News 2025: Powerful 'cannibal storm' to hit Earth today - and it could disrupt communications and GPS
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