A massive wildfire that has forced the evacuation of all 88,000 residents of the western Canadian city of Fort McMurray and burned down 1,600 structures has the potential to destroy much of the town, authorities said on Wednesday. Fort McMurray had been largely emptied of its residents by Wednesday afternoon, officials said, despite fuel shortages, snarled traffic and a highway closed by the flames in the northeastern part of the province of Alberta, the heart of Canada's oil sands region.