Transcript for Damage to nation's tallest dam forces thousands to evacuate
First we get to that breaking news out west. Incredible images this morning. Nearly 200,000 people in California told to evacuate right away after a hole was discovered in the spillway for the country's tallest dam. ABC's kayna Whitworth is there on the scene for us in California. Good morning, kayna. Reporter: Robin, good morning. As you said nearly 200,000 people evacuated. The governor issued a state of emergency after the spillway was damaged over the weekend. Can you see the dam behind me. The water is rushing over it with such force it is sending that mist into the air. And if that spillway fails, there will be nothing stopping all this water from devastating the communities below. Overnight, chaos in northern California after the emergency spillway at the nation's tallest dam was in danger of failing. There's a lot that has to be done very, very quickly. They're evacuating oroville. Reporter: A race against time for at least 188,000 residents forced to evacuate. Stuck in bumper-to-bumper traffic in their attempts to flee. Emergency crews working around the clock to prevent disaster. There is a plan currently in place which would hopefully plug that hole. That would include using helicopters to drop bags of rock into the crevice and prevent any further erosion. Reporter: Last week as millions of gallons of water poured from the dam each second, a huge hole was created. At least 300 feet wide. I am worried. I mean, this was not something anybody could have predicted or expected. You know, you call it the perfect storm. Reporter: Officials forced to use oroville's emergency spillway for the first time ever over the weekend and by Sunday, they detected another hole. Quickly prompting evacuations. This morning, although officials say lake levels have fallen and water is no longer flowing over the emergency spillway, the threat still remains. There's still a lot of unkno unknowns. We need to continue to lower the lake level. Reporter: The National Guard has been activated and officials will be out here this morning to assess the damage in the daylight. Also right next to me bulldozers are filling giant bags with Boulders that they will use helicopters to drop in and try and fill that hole. Guys. All right, kayna, frightening time right now out there. A lot of work to do to shore that up.
This transcript has been automatically generated and may not be 100% accurate.