A large tornado formed near Arnett in Oklahoma on Friday (May 4) afternoon without causing damage, but another wiped out most of the small farming town of Greensburg in southwestern Kansas, killing seven people and injuring at least 63. The funnel cloud smashed buildings, overturned vehicles and knocked out communications towers. Rescue workers were going door to door, helped by National Guard troopers. Some residents said that emergency sirens had given them about 20 minutes' warning before the driving winds hit the town. "We heard the sirens go off and we put our people down in the basement and just kind of sat huddled in the hole between the bathroom and the offices down there and listened to the house being lifted away above us. The basement stayed intact and people were all okay. We came out about an hour later to see that everything across the street was gone - so," said local resident Jeffrey Allred. The tornado was "massive", measuring up to one mile (1.6 km) wide, said Michael Lacy, a forecaster with the National Weather Service in Dodge City, Kansas. Winds were as strong as 165 mph (266 kph), he said. Emergency services workers had a difficult task. "Right now it's still a recovery effort because we are trying to go ahead and we're trying to sift through everything and, you know, clear everything as we go. So that's where we're at right now. And, like we said, it's very difficult, a very difficult situation, because communications - they're just non-existent. It's impossible right at the moment," said a local authority official. The peak U.S. tornado season runs from March through early July and they kill about 70 people every year.