The earthquake-devastated New Zealand city of Christchurch was rocked by two powerful 5.8 magnitude tremors Friday, sending terrified residents onto the streets and forcing the airport to close. The first quake struck at 1:58 pm (0058 GMT) as stores were packed with Christmas shoppers, turning their festive mood into panic as stock fell from shelves. Local news media reported people fleeing in fear as the quake and a series of strong aftershocks rattled the city. The second 5.8 quake came 70 minutes later as inner-city streets were gridlocked by people desperate to get home. "You can't underestimate the ongoing stress this has created for people," Mayor Bob Parker said, as the city continues to recover from a 6.3-magnitude quake in February that killed 181 people and destroyed much of the downtown area. One person was rushed to hospital after being injured at a shopping mall and the National Crisis Management Centre was activated. Telephone services were cut in many areas and electricity supplies disrupted, but police said there were no reports of other injuries or widespread damage. The international airport and shopping malls were all evacuated and closed after the earthquake as a precautionary measure. "I'm pretty sure we will be open again this afternoon," airport chief executive Jim Boult told Radio New Zealand. All available police units were mobilised to check on safety and damage across the city of more than 360,000 and people were urged to stay away from hill suburbs because of the risk of rockfalls. Two vacant properties were reported to have collapsed and liquefaction appeared in some of the suburbs worst hit in previous earthquakes. Scientists had warned last month of an increased probability that another powerful earthquake would hit Christchurch. "We knew to expect aftershocks and one in the range around about 6.0 was expected over the next 12 months and that appears to have arrived," Parker said. Christchurch Central City Business Association manager Paul Lonsdale told Fairfax the quakes came at the worst possible time for retailers, as people completed their Christmas shopping. "It's really the last thing we needed -- a shake just before Christmas," he said. "We've had a hell of a year really in many respects. We thought it was close to being over, but perhaps not quite." Government seismologists said both 5.8 quakes were shallow. Christchurch resident Jo Davis told Fairfax News her neighbours were screaming. "I was terrified. I guess just because it's been so long since we've had a decent one. We've had a TV and glasses fall over but no repeat of liquefaction (when earth becomes fluid) like in June so I guess it's not so bad." New Zealand sits on the so-called "Ring of Fire" the boundary of the Australian and Pacific tectonic plates, and experiences up to 15,000 tremors a year.