A 5.1 magnitude aftershock has rocked Christchurch, the biggest to hit the area since Saturday's massive earthquake.
It is understood powerful temblor, which happened just before 8am (0600 AEST) on Wednesday, caused more damage to the city's central business district and resulted in power being lost.
New Zealand Prime Minister John Key was told about the latest quake when he was on his way to inspect Kaiapoi on Wednesday morning.
Christchurch has been rattled since Saturday's 7.1 quake, the country's biggest in nearly 80 years, which smashed buildings and homes, wrecked roads and disrupted the central city.
GNS Science warned that the aftershocks may continue for some time and Christchurch City Council said the state of emergency was likely to remain in place, although it would be reassessed during the day.
Tony Stuart, a roofing contractor who lives on the Cashmere Hills, said he was in his office at his home when the latest earthquake hit.
"There was stuff off shelves, the other part of my neighbour's wall has fallen off," a badly shaken Stuart said.
"This is the biggest aftershock we have had. There is stuff falling all over the place.
"It is very scary.
"Water has even splashed out of George's bowl (his fox terrier dog)," Stuart said.
