Transcript for At least 1 killed, 3 injured after explosion rocks medical building
Next this evening, the developing headline from southern California at this hour, a deadly building explosion. The FBI is on the scene and investigating right now. People were seen in the moments after the blast. Children at a nearby preschool ordered to evacuate. You can see them holding hands there. The FBI, the ATF both at the scene, and authorities have not said what caused this explosion. Here's ABC's kayna Whitworth. Reporter: A deadly blast rocking the first floor of this southern California medical There was an explosion from the inside of fwilding going out. Reporter: Fire fighters racing to put out the flames. We heard a very loud boom and I actually felt the building shake. I could feel it while I was sitting in the chair. We actually could see where part of the building had blown out. Reporter: Children at Dale care across the street evacuated. Infants still in their cribs rolled out by staff and police. Then reuniting them with their parents at a nearby target. Investigators and hazmat are on-scene, checking hazards at this time. There were no children injured. It appears to be a building that is under construction at this time. Reporter: At least one person killed, three injured. Tonight, hazmat teams, ATF and FBI all on the scene investigating. So, let's get to kayna Whitworth with us, as well, Toni know authorities have closed down that area while they investigate tonight? Reporter: Yeah, David. It is an expansive scene. Right now, the M Boen squad is going room to room in that building, making sure the community is safe. Still no word on what caused that explosion. David? Terrifying afternoon for those children.
This transcript has been automatically generated and may not be 100% accurate.