A series of powerful tremors have rattled the earthquake-prone city of Christchurch in New Zealand, destroying a building and sending boulders tumbling down hillsides.
Many people fled buildings in panic when the 5.2-magnitude quake struck during lunchtime on Monday.
Just over an hour later, a 6.0-magnitude quake was recorded, with the epicentre four miles southeast of the city at a depth of 5.6 miles, according to the US Geological Survey.
Six people have been taken to hospitals with minor injuries from falling debris, an ambulance service said.
Two people were briefly trapped inside a damaged church, while power was cut to about 10,000 houses.
"We are being enveloped with dust. It is very, very scary," Christchurch Mayor Bob Parker told New Zealand's National Radio.
Shopping centres and office buildings were evacuated across the city, which is still trying to recover almost four months after a magnitude 6.3 earthquake killed 181 people and caused extensive damage.
A building in the city centre collapsed and minor damage occurred in buildings affected in previous earthquakes, Steven Hill, a Christchurch police spokesman, told Reuters.
"The building has been checked and been given the all-clear," Hill said, meaning no one was trapped inside.
Monday's aftershock sent boulders on the city's Port Hills tumbling towards houses.
Parts of the city, which suffered the most damage in February's tremor, suffered from flooding and liquefaction - where solid ground is turned into liquid by the force of the quake.
Dan Coward, a fire service spokesman, said they had been inundated by calls about burst pipes. He added that many people were "freaked out" by the latest jolts.
Christchurch has experienced a number of strong earthquakes since a magnitude 7.1 quake struck the city on September 4 last year.
Parts of city have been closed to the public since the February 22 quake, and one of the city's tallest buildings, the Grand Chancellor Hotel, has been declared unstable and is being prepared for demolition.
Speaking to Al Jazeera from Wellington, Caroline Ashenden, a seismologist said: "There definitely will be some more aftershocks following this earthquake.
"It's been a series of aftershocks following the September 2010 earthquake, it's probable that there are going to be more aftershocks.
"Most of the damage has been mainly done to the large buildings, which have been evacuated.
"It has been reported that there was a probability of 23 per cent of an earthquake in the Canterbury area, so the people had been mentally prepared, but it is mentally wearing them down."
The cost to rebuild Christchurch after the previous earthquakes has been estimated at about $12.2bn.
Source: Al Jazeera and agencies