Most of the oil sands operations are north of Fort McMurray and out of the direct path of the fire, which continued to move south of the city on Thursday, threatening the airport, forcing the evacuation of several small communities and showing no signs of abating.

But some operations are to the south, and one of them — the Long Lake project owned by Nexen, a unit of Cnooc, the Chinese oil company — was closed in the face of the advancing fire. The company did not offer any statistics for the lost production from Long Lake, which has been plagued by technical problems.

Production slowdowns north of the city, which is now cut off by road from the rest of Alberta, have been prompted by two factors: pipeline shutdowns because of the fire, and corporate decisions to evacuate all but the most essential employees far from the fires.

Will Gibson, a spokesman for Syncrude, which pioneered the oil sands, said the company had “reduced operations to a minimum” at its two projects and at facilities that turn the tar-like bitumen from the sands into synthetic crude oil. Syncrude’s main operation is about 20 miles north of Fort McMurray, the nearest to the city.