Canada-based Nexen Energy ULC did not give a reason for yesterday's explosion at its Long Lake facility south of Fort McMurray, in northern Alberta province.
"Our emergency response plan has been activated and response personnel, including first responders ... Are on site," Nexen said in a statement.
"We are deeply saddened to confirm one fatality and a second person is at hospital. All other personnel are accounted for."
The site was shut down "and we are stabilizing the scene."
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The Alberta Energy Regulator (AER) reported a pipeline rupture in July at the same Long Lake oil sands site.
In that incident five million liters of oil mixed with waste water and sand poured out of the site, resulting in the second largest oil spill Alberta and one of the most serious oil spills in North America.
The publicly-traded China National Overseas Oil Corporation, or CNOOC group, bought Nexen in 2013 for USD 15 billion.