As of Sunday afternoon, the suspect has not been officially identified. However, a body that could be the suspect was reportedly found inside a van linked to the case in Torrance following a police standoff.
The suspect has been described only as an Asian male between 30 and 50 years old.
The motive for the shooting – and whether it could be a hate crime linked to Lunar New Year celebrations the same night – remains unclear.
Here’s everything we know about the shooting so far:
On Saturday night, approximately seven miles east of downtown Los Angeles, visitors gathered to celebrate the Lunar New Year. The two-day festival draws tens of thousands, making it one of the largest celebrations of its kind in the region, according to the paper.
Around 10.22pm, a man entered the dance club and began shooting. Police do not know if he was targeting individuals, firing indiscriminately, or both.
Seung Won Choi, the owner of a seafood restaurant across the street from the ballroom, told the LA Times that party attendees fled the building and ran into his business, warning him to close and lock his doors.
Police arrived at the scene and found that the partygoers were already fighting to escape the building.
"When officers arrived on scene, they observed numerous individuals, patrons … pouring out of the location, screaming," Monterey Park police chief Scott Wiese told reporters Sunday. "The officers made entry to the location and located additional victims."
Los Angeles County Sheriff Robert Luna said witnesses described the suspect as a male of Asian descent, between the ages of 30 and 50, though he noted during a Sunday press conference that descriptions were not consistent between all witnesses.
By Sunday, Mr Luna was not ready to report what kind of weapon was used.
Police also believe that an incident that occurred in the nearby suburb of Alhambra may be connected to the mass shooting.
Officers were seen clearing the Lai Lai Ballroom and Studio in Alhambra around the same time that law enforcement was responding to the mass shooting in Monterey Park on early Sunday.
Mr Luna confirmed that the incident in Alhambra occurred after the shooting in Monterey Park.
The area around the Lai Lai Ballroom was cordoned off with police tape for several hours, according to CBS News.
“We are aware of an incident that occurred in Alhambra and we have investigators on scene trying to determine if there is a connection,” Captain Andrew Meyer of the Los Angeles Sheriff’s Department said during a Sunday press conference.
Mr Luna said the suspect entered the studio with a gun, but was disarmed by patrons at the business.
“A male Asian suspect walked into a dance hall with a firearm and some individuals wrestled the firearm away from him and that individual took off,” Mr Luna said during a press conference on Sunday. “Some witnesses in that area are describing a white cargo van, we don’t know though at this time if it’s connected.”
Mr Luna confirmed that the police have seized the weapon from that encounter, and said the weapon “could be” the same one used in the shooting at Monterey Park.
Fox News reports that the scene is connected to the shooting, citing sources familiar with the situation. However, those reports have not been confirmed by police.
There are no reports of injuries from the Alhambra scene.
Standoff in Torrance
Police in Torrance, California, which is located outside Los Anegeles, identified a white cargo van and surrounded it Sunday afternoon with police vehicles, including SWAT vans and armored BearCat vehicles.
Initial reports from an ABC 7 broadcast suggest that police used a drone to get a better view of the interior of the van.
The armored vehicles were positioned directly behind and infront of the van to prevent the suspect from driving away from the scene. Later, a third BearCat was moved to block the driver’s side door of the van, where the window had been smashed out.
SWAT members then opened the passenger and side doors of the vans and began a search. They dropped their guards and walked away. Reports then emerged that officers found a deceased man in the driver’s side seat of the van who had appeared to have died by suicide. It has not been confirmed if the individual in the van is the suspect.
Mr Luna also released images of the shooting suspect, which depict an older Asian man.
Aftermath & responses
The wounded were taken to nearby hospitals in conditions ranging from stable to critical, according to the LA Times.
The second day of Lunar New Year festivities has been cancelled, according to Monterey Park Police Chief Scott Weise.
“The festival that occurred Saturday also extended to Sunday. Out of an abundance of caution and reverence for the victims, we are canceling the event that’s going to happen later today,” he told reporters Sunday.
Los Angeles city controller Kenneth Mejia, the first Asian American to hold citywide office in LA, issued a statement in response to the shooting.
“Our hearts go out to those who lost loved ones tonight in our neighbouring city, Monterey Park, where a mass shooting just occurred,” he said.
Monterey Park’s demographic data shows that just over 65 per cent of its population identifies as Asian, with Hispanic identifying people making up the next largest group at 28 per cent.
Law enforcement said it is “too early” to determine if the shooting in Monterey Park was racially motivated, but told reporters “we will look at every angle as far as whether it’s a hate crime or not,” during a press conference on Sunday.
“Everything’s on the table,” Mr Luna said of the ongoing investigation. “But, who walks into a dance hall and guns down 20 people?”
City supervisor Hilda Solis confirmed that the victims treated so far have been “of AAPI descent,” but said she could not say with certainty that the shooting was the result of a hate crime.
“We’re waiting to see what our law enforcement and FBI have to say,” she told ABC 7.
White House press secretary Karine Jean-Pierre told reporters Sunday morning that Joe Biden had been briefed on the shooting and noted that FBI agents had been dispatched to investigate the attack.
Governor Gavin Newsom called the attack a “heartless act of gun violence”.
"Monterey Park should have had a night of joyful celebration of the Lunar New Year. Instead, they were the victims of a horrific and heartless act of gun violence. Our hearts mourn as we learn more about the devastating acts of last night. We are monitoring the situation closely,” he said.