The explosion happened around 8:30 p.m. on D Street, where a large group of people had gathered for a fireworks display, witnesses told Eyewitness News.
According to the Chino Police Department, detectives believe a large quantity of fireworks ignited, causing the explosion that seriously injured three adults and a child and set a vehicle on fire.
Multiple people injured in fireworks explosion in Chino neighborhood
The three adults remain hospitalized with severe injuries while the child's condition remains unknown.
Video from AIR7 showed debris scattered across a front yard and nearby street in the aftermath of the explosion.
Witnesses described a chaotic scene as people ran from the area immediately after the blast.
"Back up, back up, back up ... everybody get back!" one person can be heard saying in video recorded at the scene.
Eyewitness Gabriel Gilmore said he was inside his mother's house when he heard the blast and rushed outside to see what had happened.
"It clearly looked like there was a bunch of illegal fireworks in the trunk," Gilmore said. "I don't know how the trunk got lit up but obviously, you could see from the video that the truck hatch was busted open, and that was where the point of the explosion was."
Investigators were seen searching the neighborhood Saturday night and early Sunday morning.
The Chino Police Department is leading the investigation and is working with the Chino Valley Fire District.
Anyone with information is being asked to contact Detective Gregory at 909-334-3136.
The incident remains under investigation.