A fire that started at the Imperial Oil refinery in Sarnia, Ont., following a loud explosion just before 3 a.m. was under control a few hours later, police said Thursday.

Officials say there is no environmental danger and lifted an earlier warning to area residents to keep their windows shut and stay indoors.

There were no apparent injuries during this fire at an oil refinery in Sarnia, Ont.
(CBC)

Phil Vallance, a spokesperson with Imperial Oil, said firefighters will allow the fire to burn itself out, but didn't know how long that would take.

"That's the safest way to manage a fire of this nature," he said.

No injuries were reported and police said they had no indication of what might have caused the fire and the initial explosion.

"There were no injuries and all workers have been accounted for," said Vallance.

The part of the plant that's burning uses hydrogen to upgrade oil that's too heavy for use in gasoline and diesel, he said.

Air monitoring was being conducted in the area, but police said there was no indication of any problems.

The refinery is a 24-hour operation, but police could not say how many workers may have been in the plant at the time of the fire.