MILWAUKEE (AP) — Enbridge Inc. is seeking State Department approval for a sharp increase in its oil shipments from Canada’s tar sands region to its facilities in Superior in northwestern Wisconsin, a project that underscores the burgeoning growth in Canadian and North Dakota oil production.

Government documents show Enbridge could nearly double its capacity, indicating that the pipeline company plans to transport more Canadian oil through Minnesota to Wisconsin than previously reported. Enbridge also would move more oil to Superior from the North Dakota oil fields.

The State Department reported in the Federal Register on Friday that Canada-based Enbridge wants to boost its capacity from between 450,000 and 500,000 barrels a day to 570,000 a day. In a second phase, Enbridge is seeking to ship up to 880,000 barrels daily.

No new pipelines would be built, but the company would upgrade its pumping stations in Minnesota and Wisconsin, spokeswoman Lorraine Little said.

To ship oil from Canada to the U.S., Enbridge needs a border-crossing permit. The State Department is asking for a review of that permit and is requiring a supplemental environmental impact statement, the documents show. If all approvals are granted, Little said, the first phase would be completed in 2014 and the second in 2015.

From Superior, Enbridge ships crude to a terminal in Pontiac, Ill.

As part of the project, Enbridge is seeking to build two new storage facilities in Superior. The Wisconsin Department of Natural Resources is reviewing those plans, the agency said Friday.

Enbridge has occasionally struggled with pipeline breaks. A massive spill in 2010 required the cleanup of 819,000 gallons of oil into the Kalamazoo River in Michigan. In Wisconsin, federal regulators temporarily halted the restart of a pipeline in August until upgrades were made after a break in Adams County in July that sprayed oil 1,000 feet into the air and spilled about 1,200 barrels.

Environmentalists are critical of Enbridge’s plans. Josh Mogerman, a spokesman for the Natural Resources Defense Council, said the oil from Canada’s tar sand regions is “some of the dirtiest in the world,” because of the mining and energy required to extract it.

Little said the project reflects the changes in traditional supply sources. Instead of oil flowing north from Texas and Oklahoma, greater quantities are now coming from western North Dakota and Canada, she said.

“Our job is to rework the supply structure,” she said.