An explosion and fire at the Horizon Oil Sands facility in Canada's Alberta province has injured four workers and forced the site to suspend operations.
The blast at the plant, owned by Canadian Natural Resources Ltd, ignited the upgrader, part of the plant that converts bitumen into synthetic crude.
The company said the fire had been isolated and brought under control.
Alberta's oil sands are the largest petroleum reserve outside the Middle East.
Plumes of smoke
Oil production has been halted at Horizon Oil Sands and it is unclear when it will resume, Canadian Natural Resources said in a statement.
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