CHRISTCHURCH, New Zealand — A strong aftershock rocked terrified residents of New Zealand's earthquake-stricken city of Christchurch on Wednesday, as officials doubled their estimate for repairing the damage following nearly 300 temblors in five days.
The latest quake, which registered magnitude 5.1, was centered just four miles (six kilometers) below the Earth's surface and six miles (10 kilometers) southeast of the city. No one was reported injured, but it was felt by residents as the strongest since Saturday's magnitude-7.1 earthquake wrecked hundreds of buildings.
"My guts are just churning up here. When will this thing end? It is like living in a maelstrom," Christchurch Mayor Bob Parker said as workers streamed from the city's emergency headquarters.
"We were starting to think maybe, just maybe, we are over the worst of this, and now we have had this shocking event," Parker told NewstalkZB radio. "This is a hammer blow to the spirit of a lot of people."
After his second, closer look at the quake damage on Wednesday, Prime Minister John Key said he thought that rebuilding the city would cost more than the initial estimate of 2 billion New Zealand dollars ($1.4 billion), with at least 500 buildings already condemned and about 100,000 of the area's 160,000 houses damaged.
Treasury Secretary John Whitehead later said the full bill for quake damage could reach NZ$4 billion, with the nation's Earthquake Commission likely to pay half of that.
Key has called off a planned nine-day trip to Britain and France, citing what he called the quake zone's continuing instability.
Civil defense director John Hamilton said the safety status of some buildings would be reassessed after Wednesday's strong aftershock.
Government seismology agency GNS Science reported that more than 280 aftershocks of magnitude 3.0 or greater have struck the region in five days. Seismologist Brian Ferris said people would have felt about 150 of them.
Saturday's powerful earthquake struck at 4:35 a.m. near the South Island city of 400,000 people, ripping open a new fault line in the Earth's surface, smashing buildings and homes, wrecking roads and disrupting the central city. No one was killed and only two people were seriously injured – which authorities attributed to good building codes and the quake's early morning timing.
The city center remained cordoned off by troops Wednesday, as authorities extended a state of civil emergency for another seven days. Only building owners and workers are allowed into the central city to begin clearing up the mess – with much of the center taking on the mantle of a ghost town.
New Zealand sits above an area where two tectonic plates collide. The country records more than 14,000 earthquakes a year – but only about 150 are normally felt by residents. Fewer than 10 a year do any damage.
Associated Press Writer Ray Lilley in Wellington contributed to this report.