Tom Kloza, global head of energy analysis at Oil Price Information Service told CNBC 'We probably import more gasoline from that single refinery than any other single refinery around the world, ' he said.
Fire at Irving Oil refinery in Saint John, N.B.
Bob McVicar, a resident in the New Brunswick city, posted on Facebook that it felt like a "bed-shaking explosion".
They looked outside the window and saw black smoke and flames exceeding the height of the stacks at the refinery.
At 4 p.m. local time, residents were still being asked to stay in their homes, and nearby streets remained closed.
"We can confirm that a major incident has occurred at our Saint John refinery this morning", Irving Oil said on Twitter.
Irving Oil says it is investigating a "major incident" at the refinery, but did not provide details.
Nate Guimond, 36, said he was doing house repairs when he saw smoke.
The explosion at around 10 a.m. touched off a fire and sent thick, black smoke pouring into the air.
The Saint John Regional Hospital had issued an "orange alert", meaning it was preparing for a possible influx of patients.
"There was thick, pitch black smoke mixed with white smoke", said Guimond.
Rob Beebe felt the explosion from his apartment on Martha Avenue, a few streets over from the refinery.
In an earlier tweet, the company characterised the incident as a major one.
Irving says on Twitter that they are "actively assessing the situation" and they will share more information when it becomes available.
The refinery is near several residential neighbourhoods on Saint John's east side, about five kilometres from the city centre.