The California Department of Water Resources issued a sudden evacuation order shortly before 5 p.m. Sunday for residents near the Oroville Dam in northern California, warning that the dam’s emergency spillway would fail in the next 60 minutes.

The Oroville Dam is the highest in the nation.

An emergency alert issued on Facebook stated:

EMERGENCY EVACUATION ORDER ISSUED: Officials are anticipating a failure of the Auxiliary Spillway at Oroville Dam within the next 60 minutes. Residents of Oroville should evacuate in a northward direction, toward Chico. Other cities should follow the orders of their local law enforcement.

The emergency spillway, which is unpaved, was activated on Saturday morning to relieve the flow down the dam’s normal spillway, where a major hole appeared in recent days and began to widen. The height of the lake, once drained by drought and now swollen by recent rains and snow melt, had reached 901 feet above sea level when the emergency spillway was opened.

Aux spillway at Oroville Dam expected to fail within hour. Oroville under mandatory evacuations, could have downstream effects in Sacramento pic.twitter.com/DmHOrwQFRC — Sacramento Fire (@SacFirePIO) February 13, 2017

As Breitbart News reported in continuing coverage of the crisis, officials initially assured the public that evacuations would not be necessary, because the damage to the normal spillway appeared limited. They repeated those assurances on Saturday as the emergency spillway was used for the first time since the dam’s construction in 1968.

Now, however, local ABC News affiliate KRCR reports that state officials warn the emergency spillway could suffer a structural failure. It is not clear whether that would lead to a structural failure of the dam itself, which would be a major ecological and economic disaster.

The Sacramento Bee quoted California Department of Forestry and Fire Protection spokesperson Mike Smith: “What they’re expecting is as much as 30 vertical feet of the top of the spillway could fail and could fail within one to two hours. We don’t know how much water that means, but we do know that’s potentially 30 feet of depth of Lake Oroville.”

Authorities said Sunday afternoon that they had increased the flow down the normal spillway to 100,000 cubic feet per second, despite the damage, to relieve pressure on the emergency spillway.

The Feather River flows south into the Sacramento River. Flooding could potentially affect the Sacramento River and surrounding areas.

Update: A flash flood warning has been issued for significant parts of Butte County. The Butte County Sheriff has issued a warning: “This is NOT a drill.”

Immediate Evacuation Order – Officials: Oroville Dam In California Expected To Fail Any Moment… https://t.co/6GJBjcmYFJ pic.twitter.com/DlU9XIs2U8 — #MAGADayVarela (@dayvarelat) February 13, 2017

Update (6:53 p.m. PDT): Officials speaking at a press conference indicated that releases from the normal spillway had reduced some of the erosion to the emergency spillway and lowered the level of the lake. They were optimistic that the expected failure of the emergency spillway might be averted. They explained that they had evacuated the region out of an abundance of caution.

Update (8:30 p.m. PST): Officials are moving construction equipment into position in preparation for a daring operation to plug the hole in the emergency spillway by using rocks, which are to be dropped from helicopters.

Meanwhile, there are unconfirmed reports of looting in the largely-empty town of Oroville (later denied by law enforcement; see 11:30 p.m. update).

Houses getting looted in my neighborhood. My sons best friend home got broken in to. My house is houses down #OrovilleDam #OrovilleSpillway — Jen – Jmona (@JmonaReviews) February 13, 2017

Update (8:36 p.m. PST): The Butte County Sheriff announces that county jails are being evacuated to other prison facilities; shelters are being opened for displaced residents; and Butte College facilities and buses will be shut down on Monday. A statement on Facebook indicates the situation at the dam is precarious: “The next several hours will be crucial in determining whether the concrete structure at the head of the auxiliary spillway remains intact and prevents larger, uncontrolled flows.”

Update (8:48 PST): Mark Finan of local NBC affiliate KCRA reports that the level of the lake has dropped to near 100% capacity — just over 901 feet above sea level — such that flow has effectively ended over the emergency spillway.

At 8pm, Lake Oroville was at 901.02′. Flow is now ending over the emergency spillway — Mark Finan (@kcraFinan) February 13, 2017

That does not mean the danger is past, but it should slow the erosion of the spillway — for now.

Update (11:30 PST): A late-night press conference revealed that water had stopped flowing over the emergency spillway. Authorities plan to keep flow through the main spillway at about 100,000 cubic feet per second, with a goal of lowering the level of the lake by 50 feet, which will help the lake absorb additional runoff from anticipated storms later in the week.

Law enforcement said that there was no looting or violence in Oroville or neighboring towns, and that the rumor of looting had been started thanks to a coincidental break-in within Oroville at the time that the crisis began.

Authorities said they hoped for drier weather, as well as cooler weather (to keep snow from melting on the mountains). The maximum flow rate of the main spillway was 150,000 cubic feet per second; current inflows were 40,000 cubic feet per second. They planned to evaluate the damage to both the main and emergency spillways at first light Monday morning.

Meanwhile, evacuation orders would remain in place for nearly 200,000 people in the area below the dam.

Joel B. Pollak is Senior Editor-at-Large at Breitbart News. He was named one of the “most influential” people in news media in 2016. His new book, How Trump Won: The Inside Story of a Revolution, is available from Regnery. Follow him on Twitter at @joelpollak.