An ExxonMobil pipeline in Montana state ruptured late Friday, which spilled hundreds of barrles of crude oil into the famed Yellowstone River, prompting evacuations of nearby residents.

The company said the pipe had been shut down and the segment where the leak happened had been isolated. Precisely how much oil leaked into the river was still unclear.

The Exxon leak started sometime late Friday, with crude oil having traveled 80 miles downstream by 1 pm local time and in some places settling on the shore line, Custer County Disaster and Emergency Services Coordinator James Zabrocki told Wall Street Journal.

Nearby residents in Laurel, Montana, were evacuated in the wee hours of the morning but were able to return to their homes by 6 am, a spokesman for Laurel City Fire and Ambulance told Reuters. Evacuation orders for all of Yellowstone County have been lifted, the emergency services spokesman told Reuters.

Throughout Saturday, clean-up crews worked to lessen the impact of the spill, laying down absorbent material along the banks of the river in Billings and near Laurel to mop up some of the escaped oil, and measuring fumes to determine the health threat.

The accident happened from a 12” crude pipeline operated by ExxonMobil Pipeline Company that runs from Silver Tip, Montana to Billings, Montana. All appropriate state and federal authorities have been alerted, the company said in a statement.

At this early stage, we have no information on the cause of the incident, and we are working to determine the amount of oil released. ExxonMobil Pipeline Company deeply regrets this release and is working hard with local emergency authorities to mitigate the impacts of this release on the surrounding communities and to the environment, the company said.

A estimated 750 to 1,000 barrels of oil had leaked from the pipe for about a half-hour before it was shut down, ExxonMobil spokeswoman Pam Malek told Associated Press. Other Exxon officials estimated up to 158,982 litres of crude oil had escaped.

Meanwhile, about 1,000 barrels of crude have leaked out of ExxonMobil pipeline into the Yellowstone River, Montana Disaster and Emergency Services spokesman Tim Thennis told Wall Street Journal. He added that although no cause of the spill has been determined, it's possible that heavy flooding affecting that part of the U.S. could have played a part.

Exxon promised a full investigation into the spill, which occurred in a 12-inch pipeline, running downstream from U.S.'s major tourist attraction Yellowstone national park.

We recognize the seriousness of this incident and are working hard to address it. Our principal focus is on protecting the safety and health of the public and our employees. We will, of course, also begin a thorough investigation of the cause of this unfortunate event. We will provide additional information as it becomes available, the company said.