An earlier order that had applied to almost 30,000 people, mostly on the city's south side, was extended to tens of thousands more as flames continued to make their way into the city yesterday.
The wildfire, whipped by unpredictable winds on a day of high temperatures, worsened dramatically in a short time and many residents had little notice to flee.
Alberta Premier Rachel Notley said officials were doing all they could to ensure everyone's safety and said they were looking into the possibility of an airlift for residents with medical issues.
"When you leave ... It's an overwhelming feeling to think that you'll never see your house again," she said, her voice breaking.
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"It was absolutely horrifying when we were sitting there in traffic. You look up and then you watch all the trees candle-topping ... Up the hills where you live and you're thinking, 'Oh my God. We got out just in time.'"
Fort McMurray is the capital of Alberta's oil sands region and had a population of 61,000, according to the 2011 census. The Alberta oil sands are the third largest reserves of oil in the world behind Saudi Arabia and Venezuela.
Oil sands work camps were being pressed into service to house evacuees as the raging wildfire emptied the city. Most oil sands projects are well north of the community, while the worst of the flames were on the city's south side.
Will Gibson, a spokesman for Syncrude, which also has a plant north of the town, was himself one of the evacuees heading north away from the flames.
Gibson said he had to flee his neighbourhood via a grass embankment because the fire had already cut off the road at both ends.