Officials in Cypress County say the air quality in the area "has deteriorated to the point that it is now considered a serious life safety hazard."
The fire at the Westar landfill east of Medicine Hat started on Monday.
Early Wednesday, toxic smoke from the fire prompted officials to issue a voluntary evacuation order to 25 homes.
But by the evening, the order was made mandatory for a small cluster of home in the immediate vicinity.
The cause of the fire remains unknown but officials said it is not possible to extinguish it yet.
"There's a lot of asphalt shingles, insulation, plastic, aluminum siding, vinyl siding — all stuff that people use when they're renovating their houses," said Dennis Mann, Cypress County fire chief.
"Contractors bring it to this particular landfill. That's what's burning right now."
Officials said evacuated residents would be offered rooms at Medicine Hat hotels.
Alberta Environment and Alberta Health Services continue to monitor the situation and work with county officials.
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