At least 130,000 people in Oroville, California as well as neighbouring towns have been ordered to evacuate their homes after a massive hole was found in the emergency spillway of the Oroville Dam. Officials will try to close the hole with bags of rocks but have urged thousands of residents to go to higher ground as the situation remains dangerous.

"This is not a drill. This is not a drill. Repeat, this is not a drill," the National Weather Service said.

Residents were ordered to head north towards Chico, The Los Angeles Times reported. The mandatory evacuation also included Yuba and Sutter Counties, where evacuations were ordered for Yuba City Live Oak, Nicolaus and around the Feather River basic.

Butte County Sheriff, Kory Honea, told reporters: "I didn't have the luxury of waiting to see if all was OK. We need to get people moving quickly and to save lives in case the worst case came to fruition.

"This is a very dynamic situation. This is a situation that could change very, very rapidly."

Honea told reporters he was unsure when residents could return home. "We have to assess the safety of the spillway before we let the public back in."

KRCR reported that an evacuation centre has been established in the Silver Dollar Fairgrounds in Chico and that Highway 99 out of Oroville has been shut down to southbound traffic.

"We recognise that this has caused a significant problem with traffic, in terms of exiting the area," Honea said. Roads out of Oroville, including Highway 99, state route 70 northbound and state Route 162 eastbound, were experiencing traffic gridlock. USA Today reported that Highway 49 in Nevada County was turned into one-way traffic.

The Los Angeles Times reported that the emergency spillway had never been used before but water from rain and snow flowing into Lake Oroville at a rapid pace caused water levels to spike to emergency levels.

Officials feared a failure of the emergency spillway would lead to huge amounts of water to hit the Feather River and other waterways. The increase of water could result in flooding and levee failures miles south of the dam.

Following an unusually wet winter in California, the Oroville Lake went from almost full to overflowing in the span of a few days. By Saturday (11 February), water flowed over the dam's emergency spillway for the first time since it was built in 1968.

Bill Croyle, acting director of the water department, assured that while erosion had damaged the emergency spillway, the dam itself was structurally unharmed.