A giant X-class solar flare has provided some New Zealand sky watchers with a treat - a beautiful aurora.

Stunning pictures of the aurora lighting up the sky over Canterbury last night show a deep but hazy red and green glow.

The aurora was caused by a geomagnetic storm which stemmed from a X-class solar flare that exploded from the sun on Friday morning.

University of Canterbury Mt John Observatory resident superintendent Alan Gilmore said the aurora wasn't as vibrant as they could sometimes be.

"Not before the early morning did it actually broaden and it didn't begin until about 5am on Saturday. It wasn't spectacular but was visible in the evening and it's still there. It most likely peaked during the day yesterday."

He explained the process behind solar flares.

"Big Sun spots are actually spots where magnetism is popping through the sun's surface.

"They throw up a lot of energy and suddenly fires it off in one burst, which is what the flare is. That burst throws a cloud of charged gas which is what we call a coronial mass injection and if that hits the Earth it gets tangled up with our atmosphere."

Gilmore said the charged gas was channelled into the north and south poles.

Atoms would get thrown high up in the air, and that would create the glow. The base of an aurora was usually about 100km up in the air, and that could extend up to a further 300km at the top.

The solar flare happened 4am Friday. X-Class flares are capable of triggering planet-wide radio blackouts and long-lasting radiation storms.

- © Fairfax NZ News

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