OROVILLE (CBS/AP) — At least 188,000 people were asked to evacuate in the area near the Oroville Dam Sunday after authorities warned an emergency spillway in the structure was in danger of failing and unleashing uncontrolled flood waters on towns below.

The Butte County Sheriff’s Department issued the evacuation order at about 4:20 p.m. after the hazardous situation developed. Authorities are concerned the erosion could lead to the failure of the Oroville Dam’s emergency spillway.

MONDAY UPDATE: Tons Of Rocks Bolster Failing Oroville Dam Spillway

Evacuations orders were expanded later Sunday evening for areas of Butte and Yuba counties downstream from the Oroville Dam after one of the dam’s emergency spillway was on the verge of collapse because of severe erosion, according to authorities.

The erosion at the head of the emergency spillway threatens to undermine the concrete weir and allow large, uncontrolled releases of water from Lake Oroville, the California Department of Water Resources said. Those potential flows could overwhelm the capacity of downstream channels and levees.

The good news being reported late Sunday night was that the release of water from the main spillway had stopped water from going over the damaged auxiliary spillway.

Flows over the auxiliary spillway have ceased. 100,000 cfs continue down the main spillway. @ButteSheriff — CA – DWR (@CA_DWR) February 13, 2017

According to the Butte County officials, in addition to downtown Oroville and Thermalito, other evacuated areas include the towns of Gridley, Biggs and Loma Rica as well as areas along the Feather River south of Butte County.

Additionally, there were evacuations ordered in Yuba County including the areas around Hallwood, Marysville, Olivehurst/Linda and Plumas Lake.

Over five hours later, hundreds of cars carrying panicked and angry people were sitting in bumper-to-bumper traffic.

“The police came and told us to evacuate,” said Kaysi Levias who was with her husband, Greg, at a gas station as they attempted to flee.

Officials warned residents that the spillway could fail within an hour.

“I’m just shocked,” Greg Levias said. “Pretty mad.”

“Not giving us more warning,” said Kaysi, finishing his sentence.

“We’ve never been through this before,” said Kaysi Levias. “We have two boys and our dog. All the stuff we could fit in the trunk — clothes and blankets.”

What they couldn’t fit they piled as high as they could in their downstairs Yuba City apartment and joined the line of traffic attempting to leave the city where they had moved just three weeks ago.

When authorities offered an update at 10 p.m., both Butte County Sheriff Kory L. Honea and Cal Fire regional chief Kevin Lawson said that the release of water though the dam’s main spillway had significantly lowered the level of the lake and stopped water from going down the emergency spillway, causing more erosion.

“The efforts by DWR to lower the lake level by utilizing the main spillway has been effective. Now there is no more water going over the emergency spillway,” said Honea. “That is a good thing.”

However, despite the stability brought by stopping the erosion of the emergency spillway, there were still some concerns.

“There are still a lot of unknowns,” explained Honea. “We need to continue to lower the lake level and we need to give the Department of Water Resources the time to thoroughly evaluate the situation so that we can to make some decision as to whether or not repopulate areas.”

At an early 6 p.m. press conference, Honea said the evacuation order went out after engineers spotted a hole that was eroding back toward the top of the spillway.

“I couldn’t risk the lives of thousands of people, so we took this significant step.” said Honea.

Honea said that the crews with the California Department of Water Resources were doing everything they could to avert the crisis.

“I would rather be safe than sorry. I would rather have people moving out of the area, hopefully to safety, than to sit and hope for a solution,” said Honea.

Experts told Honea shortly after 6 p.m. that the erosion was not advancing as rapidly as had been initially thought, giving hope that the emergency spillway might not actually fail.

Honea said two inches of water is still coming over the dam, but that is significantly down from earlier flows.

Honea says there is a plan to plug the hole by using helicopters to drop rocks into the crevasse.

The California Department of Water Resources also issued it’s own statement early Sunday evening.

“The concern is that erosion at the head of the auxiliary spillway threatens to undermine the concrete weir and allow large, uncontrolled releases of water from Lake Oroville,” the statement read. “Those potential flows could exceed the capacity of downstream channels.”

Residents of Oroville were advised to evacuate in a northward direction such as towards Chico, officials said. Other cities were advised to follow the orders of their local law enforcement.

The Governor’s Office of Emergency Services activated all State sponsored California Swift Water Rescue Teams as part of the evolving Dam Emergency.

Department of Water Resources spokesman Kevin Dossey tells the Sacramento Bee the emergency spillway was rated to handle 250,000 cubic feet per second, but it began to show weakness Sunday at a small fraction of that.

Flows through the spillway peaked at 12,600 cubic feet per second at 1 a.m. Sunday and were down to 8,000 cubic feet per second by midday.

Several evacuation centers have been set up to aid those who had to leave their homes.

Silver Dollar Fairgrounds at 2357 Fair Street in Chico (small animals accepted)

Paradise Alliance Church (CMA) at 6491 Clark Road in Oroville (small animals accepted, RVs allowed in parking lot)

Elks Lodge (Paradise) 1100 Elks Lane, Paradise – (no small animals accepted, RVs allowed in parking lot)

An alternate location for residents evacuating in RVs is the Rolling Hils RV Park in Corning. Shelter for large animals is being provided at Camelot Equestrian Park on 1985 Clark Road in Oroville.

For evacuation info, Butte County residents can dial 2-1-1 from landline or cell phones. Yuba or Sutter residents can call 1-866-916-3566.

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Earlier Sunday, DWR increased the water released over the spillway to 100,000 cubic feet per second.

Water will continue to flow over an emergency spillway at the nation’s tallest dam for another day or so, officials said Sunday.

Skies are clear, and the overflow is steadily slowing, California Department of Water Resources spokesman Eric See said. It’s expected to stop by midday Monday.

Water began flowing over the emergency spillway at the Oroville Dam in Northern California on Saturday for the first time in its nearly 50-year history after heavy rainfall.

In addition to the emergency spillway, water also flowed through the main spillway that was significantly damaged from erosion. Officials said they’ll assess the damage starting Monday.

Unexpected erosion chewed through the main spillway earlier this week, sending chunks of concrete flying and creating a 200-foot-long, 30-foot-deep hole that continues growing. Engineers don’t know what caused the cave-in, but Chris Orrock, a spokesman for the state Department of Water Resources, said it appears the dam’s main spillway has stopped crumbling even though it’s being used for water releases.

“There’s been no additional erosion that they can see,” Orrock said.

Officials stressed the dam is structurally sound and there was no threat to the public.

State officials also moved most of the millions of hatchery-raised fish imperiled by muddy water flowing downstream alongside the damaged spillway after sections of its concrete walls collapsed earlier this week, the department of water resources said.

About 150 miles northeast of San Francisco, Lake Oroville is one of California’s largest man-made lakes, and the 770-foot-tall Oroville Dam is the nation’s tallest. The lake is a central piece of California’s government-run water delivery network, supplying water for agriculture in the Central Valley and residents and businesses in Southern California.

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