Christchurch is still being rocked by aftershocks 15 hours after a 7.1 magnitude earthquake which caused widespread damage.
At 4.55pm the city was hit by its biggest aftershock - a 5.4 magnitude shake centred about 10km southwest of Darfield at a depth of 10km - since the 4.35am shake which has left thousands without power and water as night falls.
Since 4.30pm the city has experienced at least seven major aftershocks, including a 4.3 magnitude quake focused only 10km southwest of Christchurch at 6.54pm, according to the GeoNet website.
By 10pm tonight there had been several further strong aftershocks.
Prime Minister John Key, who saw first-hand the devastation across Christchurch this afternoon, said it was a miracle more people weren't killed.
"This is a very, very sizeable earthquake in a very populated part of New Zealand."
Eighty police officers from Auckland will be flying in to assist with general duties and recovery in Christchurch tonight.
A Royal New Zealand Air Force (RNZAF) C-130 Hercules is currently en route to Christchurch carrying Urban Search and Rescue (USAR) personnel and dogs.
Forty two USAR personnel, their equipment and three USAR dogs from the Auckland and Palmerston North areas are on board.
Two Iroquois helicopters from No. 3 Squadron at Ohakea have also been tasked to assist in Christchurch.
They will be available to undertake aerial reconnaissance and damage assessment as required by Civil Defence.
Due to potential contamination of the fuel at Christchurch airport, a RNZAF fuel tanker is heading from Ohakea to Christchurch to supply the RNZAF aircraft.
The CBD will remain shut overnight with police manning cordons throughout the area.
No licensed premises will be open in the CBD, and members of the public will not be allowed within the cordon.
Police are urging people to stay at home and out of the central city until further notice.
There is a formal curfew in place under Section 88 of the Civil Defence Emergency Act 2002 between the hours of 7pm and 7am.
The areas affected by this curfew are the CBD block between Kilmore Street., Madras Street, Montreal Street and St Asaph Street, currently cordoned, and the shopping centre and township area of Kaiapoi.