An explosion and fire Monday at the Irving Oil refinery in Saint John, New Brunswick, could potentially affect Maine’s supply of gas and heating oil.

The facility is the largest supplier of the state’s gasoline, diesel fuel and heating oil.

The president of the Maine Energy Marketers Association said that until the scope of the damage was known, it’s too soon to guess what, if any, impact the event would have on the supply or price of heating fuel as the heating season begins.

“It’s premature to talk to suppliers about alternative purchasing decisions,” said Jamie Py, who was following news reports while attending an industry conference in Las Vegas. “But it’s a good thing it’s not January.”

The Irving refinery is the largest in Canada. It produces 300,000 barrels a day of gasoline, heating oil and jet fuel, exporting half of it to the Northeast through terminals that include Searsport, Portland and Portsmouth, New Hampshire.

In Portland Harbor, it has a major presence at the Citgo/Irving and Buckeye/Irving terminals in South Portland. A tanker was offloading product Monday at the Buckeye terminal.

That tanker can hold 230,000 barrels of refined petroleum product, according to Sean Petty, the operations manager at Moran Shipping Agencies, which serves as the agent for Irving in the harbor. At this time of year, Irving tankers holding heating oil call in Portland twice a week or so, Petty said.

Petty said he hadn’t received any information yet from Irving on the status of the refinery.

“I’m watching the news, like everyone else,” he said.

Earlier in the day, Irving Oil released a statement that said: “We can confirm that a major incident has occurred at our Saint John refinery this morning. We are actively assessing the situation at this time and will share more information when available.”

Canadian media reports showed flames and billowing black smoke coming from the refinery. Police are advising people to stay away from the refinery, and local hospitals have been notified to be ready for a possible influx of patients, according to CBC News, although no injuries were reported as of the early afternoon.

In Maine, the Buckeye/Irving terminal holds about 725,000 gallons of fuel, according to company information. It is connected to an Irving terminal in Bangor via an underground pipeline.

“There is a steady stream of tankers in the harbor from Irving,” said Mark Usinger, owner of the A.L. Griffin Inc., a ship chandler in Portland. “The port really depends on Irving now. They are in constant rotation.”

The company doesn’t publicly release shipping information, but has in the past estimated that three out of five vehicles in Boston run on Irving gasoline. Five years ago, the New England Petroleum Council said 70 percent of Maine’s gasoline comes from the Saint John refinery, although it also can receive product from refineries in New Jersey and Philadelphia.