WHITE HORSE, S.D. (AP) — Record-breaking flooding has caused dozens of people to evacuate from a reservation in northwest South Dakota.

Officials on the Cheyenne River Sioux Tribe have declared a state of emergency and urged residents to voluntarily evacuate before the Moreau River crests Thursday.

The Argus Leader says about 50 people have been evacuated so far, some by helicopter. Some residents concerned for their livestock and property have refused to evacuate. Tribal chairman Harold Frazier says residents should take the threat seriously because the river has never been this high and is rising.

The National Weather Service says the river is expected to crest at more than 30 feet Thursday night. Severe flooding has also swamped the sprawling Pine Ridge Reservation in southern South Dakota, trapping some in their homes.

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