The fire, named the Delta Fire, is burning in the Shasta-Trinity National Forest with no containment.
On Thursday afternoon, a TV station reporter tweeted that he had counted five homes that were destroyed in the fire. At least four tractor trailers caught fire along the stretch of I-5 and 17 big rigs were simply abandoned in the roadway. Interstate 5 usually swarms with trucks and traffic as it winds its way through California.
"Shasta County Evacuations: Numerous structures are threatened, and the Shasta County Sheriff's Office has issued mandatory evacuations for residents along the Interstate 5 corridor from exit 707 at Vollmers north to exit 714 at Gibson".
It was 8 square miles (21 square kilometers) on Wednesday.
"They were the largest fires, and as soon as you bought those fires under control, they could re-deploy those firefighters to other areas within the larger area.up to Oregon, Washington and then down to Southern California".
BREAKING: The #DeltaFire has forced the closure of I-5.
While New Zealanders fighting fires in OR to the north had been glad of their Swanndris to keep them warm at night, in California the heat was "unrelenting", 30C overnight and 40C during the day.
A firefighter sprays the smoldering remains of a vehicle on Interstate 5 as the Delta Fire burns in the Shasta-Trinity National Forest, Calif., on Wednesday, Sept. 5, 2018. The state's fire agency says it's nearly out money, having spent $432 million to fight fires through August and the "official" fire season has only just begun.
Before the highway is reopened, authorities have to check the safety of the pavement and cut down burned trees next to the road - some of them 70 feet tall - that might be in danger of falling down.
Less than 24 hours after the blaze broke out Wednesday in the Shasta-Trinity National Forest, the Delta fire had grown to more than 15,000 acres.
Caltrans said Friday they expect Interstate 5 will remain closed until Sunday, when they will re-assess the situation. It was moving rapidly but was still far from any large towns. "Whatever occurred here was probably pretty ugly for a while".
"It isn't a lot of people", he said.
Shasta County communities are still recovering from a devastating blaze this summer that killed eight people and incinerated hundreds of dwellings in and around Redding.
Amtrak delayed its Coast Starlight service from Sacramento to OR because of the fire. It was only fully contained last week.