Marc Smutny was doing landscape work at Parkway RV Resort and Campground before 6 p.m. when he heard an explosion on the 5 Freeway.
"I heard probably three explosions," Smutny told the Los Angeles Times in a phone interview.
Smutny had heard a FedEx big-rig careening head-on into a charter bus full of high school seniors from the Los Angeles area, killing nine people. The students were set to tour Humboldt State University.
Both the drivers of the bus and the FedEx truck were killed. The seven other fatalities were passengers on the bus.
The California Highway Patrol said the FedEx truck was traveling southbound when it crossed the median and collided with the northbound bus.
Smutny ran to the scene and saw flames engulfing the FedEx truck and the white charter bus. Flames flew as high as three stacked fire trucks, he said.
"It was insane. The bus was engulfed in flames, smoke in and out of the front," Smutny said.
"The bus looked like it took most of the hit. … The flames were completely engulfing both. It was horrible. Like basically, it looked like a FedEx truck took a bad left turn and hit the tour bus head-on."
"We thought it was a propane fire," he said.
CHP Officer Tracy Hoover said the crash occurred around 5:40 p.m. For unknown reasons, the FedEx truck crossed over the center median covered by foliage, she said. The truck first sideswiped a white passenger vehicle, then hit the charter bus carrying 48 people "head-on," Hoover said.
Nine people were declared dead at the scene, she said.
Hoover said the bus was carrying students from the South L.A. County area who attended various high schools and were visiting colleges.
She estimated that more than 30 people were injured. At least one person suffered from "severe burns" while other students had "cuts, scrapes, minor burns and contusions." Flight and ground ambulances took an unknown number of victims to various hospitals.
In addition to the students, three chaperones and a driver were aboard the bus, Hoover said. As of about 9 p.m., she said, all passengers had been taken from the scene, but coroner's officials had not arrived.
"We're just starting the investigation," she said.
Both northbound and southbound lanes of the 5 Freeway in the area are expected to be closed until around 7 a.m. Friday, she said.
Parents are urged to visit the Red Cross to get information about their children.