An object thought to be debris from a space station was seen by many flashing through the southern sky on Tuesday evening.

An object which exploded over the South Island on Tuesday night is believed to be debris from supplies sent to the International Space Station, not a meteor, an expert says.

What was first thought to be a large meteor exploded over the South Island on Tuesday night, sparking a flurry of phone calls to police.

It was spotted up and down the island when it hit Earth's atmosphere and exploded about 6.30pm.

NICOLA EVANS/SUPPLIED Nicola Evans sent in this shot of the object over Blenheim.

Earth and Sky astronomy guide Kristian Wilson, who works at the Mt John University Observatory, clarified initial reports on Tuesday night.

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"It could possibly be debris that's been sent up with the International Space Station," he said.

AMBER HANNAH/SUPPLIED Amber Hannah, who took this photo at Lake Hawea, said the object "passed the moon and burned red and broke up as it hit the atmosphere".

The material may have been sent up on a "cargo ship" launched on Monday.

"So a Falcon 9 – It's basically supplies for the space stations," Wilson said.

"We now believe it's not a meteor."

Paul McKenzie Paul McKenzie took this shot in Blenheim.

The object's arrival in the South Island's skies was consistent with a recent trip to the space station.

"Most of the time they [the trips] are predicted. This one wasn't, or not to our knowledge, but they do this often," Wilson said, adding the trips were made about every six months.

"It's not often we get to see this debris."

Dale Colliss This picture, of what is believed to be debris, was sent in by Dale Colliss. He snapped the pic while driving from Oamaru to Kakanui.

Wilson believed the debris was 13 by 5 metres.

"So it's not exactly small."

If it was to hit earth it would have been about the size of a fist by the time it got here, he said.

Some people called police thinking it was an object on fire or a "big flame in the sky".

Did you see it? Send your photos and video to newstips@stuff.co.nz

Earlier, when it was thought to be a meteor, astronomer Natasha Gardiner said it exploded into four pieces after hitting earth's atmosphere.

Some thought it was a flaming object or a "big flame in the sky".

"We have been up here on Mt John for years and we have never seen one this big.

"We saw it soaring across the sky and then it exploded and went in four different directions."

Gardiner guessed it would have burned down to the size of a fist.

"Normally they are about the size of a grain of sand."

A large meteor over Russia several years ago created shock waves that smashed windows, injuring people, she said.

"We were a bit a little bit concerned initially to be honest."

Gardiner said it was unlikely to have hit the ground.

Police said there were "multiple reports of colourful lights flashing across the sky". One Otago caller thought it was a flare.

Residents in Nelson, Blenheim, Wanaka, Cromwell, Waimate, Dunedin, Alexandra, Karitane, Central Otago, Oamaru, Timaru, Mosgiel, Ravensbourne, Middlemarch, Hawea Flat, Ashburton, Mt Cook, Marlborough, Greymouth, Kaikoura and Palmerston reported seeing the object on WeatherWatch.

Witness Anna Cox saw it flying over Mt Cargill in Dunedin and said it was "massive".

She was "too amazed" to get a camera.

"[I] thought it was a big firework until [I] realised how high up and how big it was… [it] burned for about 30 seconds before dying out about 100 metres above the summit."

Hayden Brown saw the "bright streaking" object flying over Timaru.

He saw if for about 15 seconds before it went behind cloud. He phoned Christchurch Airport's air traffic control and was told there were no aircraft in the area.

"Very cool," he said.

Sarah Green was in the middle of a military fitness class in Argyle Park, Ashburton, when the object blazed overhead.

"It proved an amazing distraction ... and gave us a cherished breather. One of the most beautiful sights I have seen," she said.

WHAT IS A METEOROID?

A meteoroid is a small particle from an asteroid or comet orbiting the sun.

A meteor burns up after hitting the earth's atmosphere – also known as a shooting star.

A meteorite survives the trip through the atmosphere and hits the ground.

