At least 20 children were injured after a stairwell collapsed at a paintball center in San Diego Saturday evening. The incident happened around 8 p.m. at Total Combat Paintball in the 1600 block of Main Street, according to ABC affiliate KGTV. It was unclear what caused the stairwell platform to collapse, authorities said. The children's injuries were minor to moderate, according to the San Diego Fire Department PIO. Authorities said parents arrived at the scene to be reunited with their children. It was unclear if anyone was transported to a hospital. No further information was immediately available.