A geologist has explained the flash of light that lit-up skies following yesterday's 7.5 magnitude earthquake.
The quake has measured as being among the biggest to ever hit New Zealand - the most severe to hit was back in 1885 in the Wairarapa with a magnitude of 8.2.
Professor Mark Stirling said scientists agree the flash of light is connected to earthquakes, but they have several theories as to how the phenomena forms.
"It's to do with ionisation - fault rocks are rubbing together, and producing electrical discharge, which goes out into the atmosphere as light, and ionises it."
"There is of course this healthy scientific debate about the exact cause" he said.
He said the earliest was observed in New Zealand in 1888 during the Hope fault line near Hanmer Springs.
A more recent example was Italy's 2009 quake.