On 22 February 2011, a 6.3 magnitude earthquake struck Christchurch shortly before 12.50pm at a shallow depth of four kilometres. Several aftershocks were reported, some registering at a 5.6 magnitude. This was the second major earthquake to hit the city; the previous quake occurring on 4 September 2010 and registering at a 7.1 magnitude. Civil defence declared a category 3 emergency, the highest possible for a regional disaster.
The Christchurch earthquake caused 185 deaths, 6 659 major injuries (in the first 24 hours) and extensive damage to infrastructure and buildings. Multiple buildings collapsed, with approximately 10 000 homes needing to be rebuilt, 3 500 homes to be demolished (from the September 2010 earthquake), burst water mains, flooding and liquefaction in the city, power outages across the city, cracks in many roads, damage to the port, and more than 4 500 vehicles stranded in the city centre during the recovery period. The Christchurch airport was open only for emergencies and schools were closed.
The Department of Foreign Affairs Australia registered 8 000 Australians as being in the Canterbury region during this period, with 350 in Christchurch. One Australian was among the confirmed 185 who died in the earthquake.
During the rescue effort, 600 Australian emergency services workers including, police, search and rescue, medical and forensic experts assisted with the recovery efforts.