A global effort is refining the search for a meteorite believed to have struck the earth near Dunedin last week.

University of Otago master's student Thomas Stevenson is stitching together 1005 aerial images he took with a drone to re-create a 4sq km search area on a Lee Stream farm — southeast of Middlemarch, northwest of Outram — which he hopes will reveal the crash site.

As Otago geology students searched the farm believed to be where the meteor crashed about 10.50pm on Sunday, August 28, Stevenson put his drone up to survey the ground.

Scientists are searching for a meteorite that fell to the ground after a spectacular fireball lit up the sky over Otago. Video / Supplied

The map of the area he was creating would be finished today.

Yesterday, after reviewing 881 of the 1005 photographs without uncovering signs of a meteorite, he remained optimistic it would be found, he said.

A 1kg meteorite, or a rock the size of a fist, would be expected to create a crater with a 1m diameter, Stevenson said.

However, estimates of the size of the fireball had increased and now ranged up to 30kg.

A meteorite that size would create a crater of several metres across, he said.

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The meteorite fell somewhere in the area southeast of Middlemarch and west of Outram. Image / Fireballs Aotearoa.

If found it would be only the third time in New Zealand that a meteor had been recovered after being seen falling to Earth, he said.

There was a very good chance that the meteor was big enough not to have burned up on its descent.

An image captured at the Beverly-Begg Observatory, in Robin Hood Park, Belleknowes, showed an "absolutely massive fireball".

"It's actually so big that the camera didn't register it as a meteor at first — it thought it was looking at the moon."

The "fireball phase" for most meteors ended between 80km to 30km above the ground, but this fireball was visible until it was 15km above the ground.

"This thing fell so fast that the fireball phase of its flight lasted about 5secs and there was another 1sec that was in 'dark flight' and we couldn't see it."

Much of the dark flight analysis was being done in Ontario, Canada where Western University meteor physics postdoctoral researcher Denis Vida was doing all the "hard number crunching for the Global Meteor Network", helping to pinpoint the location of the meteorite.

An updated weather model from MetService had refined that work, and the international group looking for the meteorite now believed it hit the ground 500m east of where the modelling initially indicated.

Winds in the area at the time would have pushed the meteor near the end of its flight.

Another search of the Lee Stream area was planned, but it was not yet known when.

"It's just a question of getting enough people and enough time to do it properly," Stevenson said.

- by Hamish MacLean, Otago Daily Times