A massive storm is set to intensify over New Zealand after already blacking out thousands of homes, uprooting trees and collapsing a stadium roof under tonnes of snow. Another heavy dump of snow is expected in Southland and Otago in the South Island on Monday night and Tuesday, adding to the thick blanket that fell last weekend. Buildings have been damaged by the weight of the snow and on Saturday morning dozens of tennis players evacuated Southland Stadium when its roof partially collapsed. Local Jason Smith was standing outside the courts when the doors in front of him were pushed open. "It was like a big explosion and I remember seeing what looked like a panel off the roof fly past me a couple of metres away," Mr Smith told The Press. "I thought it was a bit of an earthquake in the beginning, then realised nothing else was moving and just ran." Tennis coach Andre Van Rooyen said his biggest fear was people getting trapped. "It was just lucky, I really think there could easily have been a few deaths," he told The Press. "It was just carnage, it looked like a tornado coming as the roof collapsed." The cave-in again sidelined a team of Brisbane netballers during their NZ tour. The girls were originally due to play in Christchurch, but the match was transferred to Southland Stadium due to the devastating earthquake there earlier this month. Now the match has again been cancelled and the Aussie netballers are heading to Dunedin and Queenstown ... hoping disaster doesn't follow them there, too. The North Island was hammered by strong winds over the weekend that cut power to about 52,000 customers, caused flooding and whipped up eight metre swells on Auckland's west coast. In Auckland, New Zealand's most populated city, hurricane-force winds reached 120km/h, uprooting trees, demolishing buildings and ripping roofs off homes, weatherwatch.co.nz analyst Philip Duncan told AAP.