CHRISTCHURCH (AFP) - A series of powerful earthquakes, including one of magnitude 6.0, rocked New Zealand's Christchurch on Monday, bringing further destruction to the quake-scarred city. More than 50 buildings collapsed and there was severe disruption to electricity and water supplies in the city, where residents are still recovering from a deadly 6.3 earthquake in February that killed 181 people. "We are in a serious situation," said Bob Parker, the mayor of Christchurch. National Crisis Management Centre controller said there were no reported fatalities from the latest tremors?.