Powerful earthquakes have again rocked Canterbury on Monday, causing injury and damage.
Two people are in Christchurch Hospital with serious injuries, while another 44 were treated at the emergency department and discharged, a spokesperson for the Canterbury District Health Board said.
Power has been cut to thousands of households and some are without water, roads and bridges have been damaged, and there is flooding and more liquefaction.
The strongest quake, measuring 6.0 at 2.20pm, was felt widely in the region and occurred 10km southeast of Christchurch at a depth of 9km.
The tremors began at 7.37am and continued throughout the day, including a short, sharp 5.5-magnitude jolt at 1pm, which was felt in other parts of the South Island from Hokitika to Dunedin.
Canterbury has been hit by strong earthquakes since 4 September last year when a magnitude 7.0 quake occurred, followed by the 6.3 quake on 22 February which killed 181 people and caused severe damage to central Christchurch.
Some buildings already damaged in the February quake and due for demolition collapsed on Monday.
Canterbury Earthquake Recovery Authority demolition manager Warwick Isaacs estimates that up to 50 city centre buildings were damaged or have collapsed.
Christchurch Cathedral suffered further damage, while the tower of the historic Timeball Station in Lyttelton has collapsed.
The quake caused extensive damage in the hill suburbs of Sumner and Redcliffs, bringing down large boulders and forcing people to leave their homes.
An extra 140 police remain in Christchurch from throughout the country following the February quake and will patrol the city and provide information to welfare services.
Police have warned people not to try and take advantage of the quakes to commit crime in the central city, as judges are taking these matters very seriously.
The Fire Service has stood down Urban Search and Rescue Teams but expected a number of callouts for assistance with liquefaction, flooding, burst pipes and possible gas leaks.
Schools and early childhood centres have been strongly advised by the Ministry of Education to stay closed on Tuesday.
Christchurch mayor Bob Parker concedes the latest tremors may be enough for more residents to join those who have already relocated to other cities in New Zealand and Australia.
Thousands without power
Up to 20,000 customers are facing a near freezing night without power. Outages are concentrated in the eastern parts of Christchurch, including Sumner, Red Cliffs and New Brighton.
Anyone planning to leave their home is advised to switch off the mains power before they go.
Lines company Orion said it is expected that power would be restored to all customers on Tuesday.
Residents urged to boil water
The Canterbury District Health Board has warned that water used for drinking, brushing teeth or food preparation should be boiled before being used.
The Christchurch City Council says water has been restored to homes in New Brighton and North Shore, but residents in Sumner, Redcliffs, Mt Pleasant and Lyttelton are without running supplies late on Monday night.
Water tankers have been stationed on the corner of Wainoni Road and Breezes Road, and on the Sumner side of the causeway at the junction of McCormicks Bay Road and Main Road.
Crews will begin reconnecting waste water systems on Tuesday. In the meantime, residents who have a chemical toilet or a portaloo are advised to use them and people should only use their toilet sparingly.
Some parts of the city sewage has mixed with silt and should only be handled with waterproof gloves, gumboots and a dust mask.
A welfare centre has been set up at Cowles Stadium, 170 Pages Road in Aranui, which can house up to 300 people.
Civil Defence says special support is also planned for Lyttelton.
People who have doubts about access or security of their homes are also advised to stay with friends or family.
The Government helpline is: 0800 779 997.
Stay off roads, police warn
Police have appealed for motorists to stay off Christchurch roads, as many are affected by flooding and liquefaction.
The Old Waimakariri, Gayhurst Road, Bridge Street and Martindale bridges were closed on Monday evening, Civil Defence said.
Christchurch mayor Bob Parker said work is under way to confirm that the roading network is basically solid and a traffic guidance will be issued for travel on Tuesday morning.
The Lyttelton Tunnel is open.
Text rather than phone
People in Christchurch and those trying to contact them are asked to text message rather than make phone calls to reduce congestion.
The telecommunications network in the city stood up well during Monday's quakes, but some cellphone sites are running on battery power due to electricity outages.
The emergency 111 system is working well, with usual back-ups in place.
People who have analogue phones which plug into the wall should use them as they can work without electricity.
Flights have resumed in and out of Christchurch after the airport was briefly evacuated on Monday afternoon, but travellers are warned to expect delays.
There is no structural damage to the buildings, the Fire Service said.