One of the most powerful cyclones on record began pounding Australia’s northeast coast on Wednesday, threatening tourist cities and sending people scrambling to find refuge after police turned them away from overcrowded shelters. Cyclone Yasi, packing winds of up to 300 km (186 miles) an hour near its core, started to come ashore along hundreds of km of coastline on Wednesday night, giving a foretaste of a storm center described by authorities as "terrifying".