New Brunswick city resident Bob McVicar wrote on Facebook that it felt like a "bed-shaking explosion". Five people with injuries from the explosion were treated at Saint John Regional Hospital, and all have been released, Horizon Health Network said in a statement.
We will update as more information becomes available.
Saint John Mayor Don Darling said on Twitter: "This is obviously a live event. when we know more, you'll know more".
Irving Oil is a major supplier of oil to the northeastern part of the United States.
The company exports more than half of that supply to the US.
Nate Guimond, 36, said he was doing house repairs when he looked outside and saw the scene.
Saint John Police tweeted that they were responding to the incident, and asked people to stay away from the area. Thank you to all first responders who are working in response to this incident.
When he walked outside, he noticed black smoke coming from the refinery, so he hopped into the auto, drove down the corner and saw fire about 30 metres high. Streets in the area have been closed as authorities monitor the situation.
He said: "We probably import more gasoline from that single refinery than any other single refinery around the world".
Black smoke and flames can be seen for miles, higher than the refinery's stacks.
Mark Melanson and Jocelyn Legassie were sitting at the Tim Hortons on Hickey Road, about three kilometres away from the refinery, when they heard a popping sound.
The Irving Oil Refinery is a Canadian oil refinery located in Saint John, New Brunswick.
He chose to drive by the refinery, and said he was nearby when he felt the vibrations of what he assumed must be a second explosion.