The earthquake was magnitude 6.3 and struck at a depth of 5km, 10km south-east of Christchurch CBD. It was shallower and closer to Christchurch than the 7.1 magnitude quake on September 4, which was recorded at a depth of 10km, near Darfield.
Three Geonet monitors in the Christchurch CBD recorded much worse ground shaking than was felt during the original September 4 quake. It was expected to have caused a fissure in the ground under its epicentre in Lyttelton.
The quake has caused devastation. Emergency services are reporting multiple fatalities, serious injuries and extensive structural damage to buildings. Hospitals throughout the South Island have been cleared to take in a flood of patients from Christchurch.
Fires are breaking out in the city centre. Reports are still emerging about people who remain trapped. The iconic Christchurch Cathedral, which survived the original September 4 quake, has collapsed. Hospitals throughout the South Island have been cleared to take in a flood of patients from Christchurch.
Civil Defence Minister John Carter said there will be continuous aftershocks in the wake of the quake.
He advised people who could not cope with the shocks to leave the city in the short term. A Geonet spokesman said the train of significant aftershocks would last about two days.
The Earthquake Commission is expected to treat the quake as a new earthquake, which means it will accept claims of damage for the next 90 days. As at 17 February the EQC had received 181,107 claims and paid out $740 million to claimants from the September 4 quake. This quake has caused much more significant damage.
Footage taken after the disaster is already on Youtube. The Twitter hash-tag for updates on the disaster is #eqnz.