The incident was reported about 10:45 p.m. in the 1200 block of Lynwood Drive, said Capt. Rich Lawhead, spokesman for the San Bernardino Police Department.
Officers from multiple agencies arrived to find "multiple victims down and a very chaotic scene," the captain said, adding that "the crowd was uncooperative."
The injured men, women and teenage boy were transported to three hospitals, according to Lawhead. Two were listed in critical condition. Six others suffered non-life-threatening wounds.
Heartbroken over the shooting in San Bernardino. Praying for the injured and the entire community. Thank you to the law enforcement officers and first responders in the scene.— Kamala Harris (@SenKamalaHarris) September 3, 2018
"It does appear that they were shooting back and forth. But other than that, all I can tell you is that multiple weapons were fired," Capt. Rich Lawhead said.
Authorities had initially said 10 people were wounded. Police attributed the erroneous number to a hospital miscount.
Witnesses told investigators that the wounded were in the complex's common area, possibly playing dice, when the gunfire erupted.
Multiple handguns and rifles were fired in the shooting, police said. None of the weapons were recovered.
No arrests have been made. Descriptions of the shooters were not available.
In a tweet, Sen. Kamala Harris said she was "heartbroken" over the incident.
"Praying for the injured and the entire community," she added. "Thank you to the law enforcement officers and first responders in the scene."
Authorities said it was unclear what led to the shooting, and that witnesses and victims are not cooperating with investigators.
Police said they are looking into whether the shooting was gang related.
Anyone with more information was urged to call (909) 384-5655,