Wright said it's unclear if the number of people or the construction of the platform contributed to its collapse. All are expected to survive.
The incident happened at Vault PK at 1699 Main Street.
City building inspectors arrived to survey the scene Saturday night and will continue to investigate the collapse on Sunday.
Twenty-one children and two adults were hospitalized. One parent said the stairwell collapsed when dozens of children ran up and down to get pizza from a loft.
A parent told NBC 7 they recieved a phone call from Vault PK alerting them that his son suffered a bloody nose.
Joe Saari, a parent of two children, who suffered minor bruises due to the collapse, said that when he and his wife dropped off their kids at the facility, there were 100 to 150 kids at the center.
Besides paintball, the warehouse includes trampolines and bouncy houses. However, none of them were injured.
According to the San Diego Fire Department, the injuries were considered minor to moderate.
Zachary Smith told the Los Angeles Times that it was "a freak accident" that could have been avoided because the structure didn't appear to be able to hold such weight. On the particular night that the incident took place the gym was open for children between the ages of five and 14. Children huddled nearby in groups, some with parents.