California dam
Water spilling from the California damReuters

Thousands of residents in northern California were asked to evacuate their homes on Sunday evening after the United States' tallest dam suffered damage posing threat of unleashing flood waters on towns just below it.

The California Department of Water Resources on Sunday afternoon said that the emergency spillway of the Oroville Dam in Northern California could fail within a span of an hour unleashing uncontrolled flood waters from Lake Oroville. The department also added that people living in the downstream areas are required to leave their homes as soon as possible.

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The officials, however, earlier on Sunday had said that the structure of the dam was sound and that there was no threat to the public.

The Butte County Sheriff's office advised the residents of Oroville to head north toward Chico and said that other cities should follow orders from their local law enforcement agencies. Orovill harbours around 16,000 people.

"Immediate evacuation from the low levels of Oroville and areas downstream is ordered. This is NOT A Drill. This is NOT A Drill. This is NOT A Drill," sheriff said in a statement posted on social media.

The residents in the valley floor, including Marysville, a city of 12,000 people, were asked to immediately evacuate their houses and take routes to the east, south, or west and avoid travelling north toward Oroville by the Yuba County Office of Emergency Services, according to Reuters. Reports state that a lot of Sikhs also stay in the affected region.

The California Department of Water Resources said that it is releasing around 100,000 cubic feet per second from the main, heavily damaged spillway to try to drain the lake.

California Governor Jerry Brown asked the Federal Emergency Management Agency on Friday to declare a major disaster because of flooding and mudslides brought on by the storms.