The governor of the U.S. state of Montana has declared an emergency in seven counties affected by an oil spill into the Yellowstone River from a ruptured pipeline.

Governor Brian Schweitzer issued the order late Tuesday. It lists the ExxonMobile oil company as being responsible for the spill.

Exxon officials have said they have seen oil only as far as about 40 kilometers downstream, but the governor, who is a soil scientist, said Tuesday he believes the oil may have already traveled much farther downriver.

The governor toured the flooded river on Tuesday, where the current is making it difficult for emergency workers to remove the oil and oil-covered debris. The governor urged people downriver to report any oil they see. Exxon has promised to take financial responsibility for the spill.

Federal officials have demanded that Exxon repair and re-bury its pipeline more deeply than before. Exxon says it has up to 200 people on the ground scanning the river for oil and cleaning up what they find.

The pipeline in the western U.S. state ruptured last week, dumping about 1,000 barrels of crude oil into the swollen river.

The spill from the ExxonMobil pipeline late Friday near the town of Laurel sent oil many kilometers downstream in a waterway known for its superb fishing. Residents near the rupture were evacuated as a precautionary measure. The pipeline has been shut down since late last week.