The New Zealand city of Christchurch has suffered its most damaging aftershock since a powerful earthquake at the weekend. The 5.1 magnitude tremor cut power, further damaged buildings and sent frightened residents into the streets. Regular aftershocks have hit the area since Saturday's 7.1 quake, but yesterday's was more damaging because of its shallow depth. More than 100 aftershocks have rocked the area since Saturday. Some of Christchurch's most historic buildings have been damaged beyond repair and are to be pulled down. New Zealand's ministry of civil defence has warned that an aftershock of up to 6.0 magnitude is possible in the next few days. A state of emergency has been extended for a further week.