Investigators were still searching for a suspect or suspects after three men were killed and nine other people were taken to hospitals following a shooting Tuesday night at a costume party at a home in the Southern California city of Long Beach, fire officials said.

Officials said those injured were seven women and two men ranging in age from 20-49. They warned that the number of wounded people could rise because they didn't know if people at the party had brought themselves to the hospital.

Five of the injured people were considered "immediate," or with injuries that paramedics believe could potentially be life-threatening, Jake Heflin, public information officer for the Long Beach Fire Department, said.

"It looks like it was a party, some type of a Halloween-type costume party and that seems to be where the shooting occurred," he said, according to video from NBC Los Angeles.

Long Beach Police Chief Robert G. Luna added Wednesday morning that the costume party was a Halloween, birthday hybrid, and it appears that the 25-30 people who were there when the shooting happened worked together somewhere outside Long Beach.

Firefighters responded to the shooting at Seventh Street near Temple Avenue at about 10:45 p.m.

At 10:44 pm, @lbfirefighters responded to shooting at a residence on the 2700 block of 7th Street. An MCI was declared with a total of 12 patients. 3 confirmed fatalities (adult males) 9 patients transported to local area hospitals. 5 immediate & 4 delayed. PIO onscene. pic.twitter.com/k8txxNqZfL — Long Beach Fire (CA) (@LBFD) October 30, 2019

Heflin said the shooting took place at a residence behind a storefront, and the three men who were pronounced dead were discovered in the backyard. Luna said the scene was "horrific," adding there was "blood everywhere."

He said Wednesday morning that witnesses said a male suspect fled in a dark-colored vehicle. Investigators don't know if other people were involved, and have not determined a motive, but believe the party was targeted.

Police said in a statement Wednesday that “unknown suspect(s) opened fire on the group from an alley located behind the residence,” hitting the 12 victims. The preliminary description of the suspect is a male wearing dark clothing and with his face concealed.

Luna said the gunman fired "almost indiscriminately, not caring who he hits."

"We’re just very anxious to find out why would somebody do something like this. This is not reflective of our community of Long Beach — this does not happen here," Luna said, adding that he has been with the department for more than 30 years and cannot remember an incident with a dozen victims.

"I know people have information as to who this coward is. I would like them to come forward," Luna said.

Long Beach firefighters responded to shooting at a residence on the 2700 block of 7th Street. Long Beach Fire

Police said that at this stage in the investigation “detectives do not believe this was a random act of violence, nor is there any indication that this incident is gang-related.”

A man in the neighborhood told reporters that just before the violence, he was on his way to a liquor store in the area, which he said was normally quiet. The store was closed, and he was walking home when he said he heard around 20 shots and ran.

"It didn't seem real. I thought I was dreaming," he said. "It was continuous shots," he added.

Long Beach is a city on the southern tip of Los Angeles County.

Those wounded and taken to hospitals were described by police as ranging in age from 20 to 49, and they live in the cities of Anaheim, Hawthorne, Cudahy, Gardena, Compton, Lawndale and Los Angeles.