"Everyone is on edge here anyway," said Rhys Taylor, who said he could hear sirens and see helicopters flying over Christchurch. "Obviously, power's out -- sort of all over the city at the moment -- and phone lines are down."

Police evacuated sections of the city's central business district after reports of a possible gas leak, police said. Several bridges in the city were closed as a precaution.

The first quake -- a magnitude 5.2 -- was centered 9 kilometers (5 miles) east-southeast of Christchurch at a depth of 11 kilometers (6.8 miles), according to USGS. The quake took place at 1 p.m on June 13.

The second quake -- a more powerful 6.0 tremor -- struck at 2:20 p.m., roughly 13 kilometers (8 miles) north-northeast of the city at a depth of 9 kilometers (5.6 miles).

And at least one smaller quake followed. A magnitude 4.6 quake struck at 2:40 p.m. about 11 kilometers (6 miles) east of Christchurch and at a depth of 12.5 kilometers (7.8 miles), according to the USGS.

The quakes came nearly four months after a 6.3-magnitude temblor struck the same area, killing more than 180 people.