Officials say at around 9 p.m., Oakland police and fire responded to Grand and Euclid Avenues to a report of multiple shootings where a large crowd was gathered.
UPDATED STORY: 15 shot, 1 assaulted at Juneteenth celebration near Oakland's Lake Merritt, police say
Oakland police say that earlier around 5,000 people were near Lake Merritt for the celebration and it was peaceful until around 8:15 p.m. when an illegal sideshow happened near Grand and Bellevue Avenues. A fight then broke out and multiple shots were fired, hitting several victims.
ABC7 News spoke with one witness who was at the scene.
"We were all celebrating, there were sideshows, couple of fights that were going on - next thing we know, we all thought we heard fireworks, so we ran from the direction," said witness Tamia Robinson. "Next thing you hear, another 'boom, boom, boom, boom, boom' from the other side of the lake. We come down here, walking, and my sister sprints across the street, where she's seen one of her friends were laying out."
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Police say four gunshot victims were transported to a hospital. Their conditions are unknown at this time.
A number of other injuries were also reported. Authorities say the incident could be a possible "mass casualty" event.
"At this time, there are no reports of fatalities, and the exact number of those injured is still under investigation. No arrests have been made in connection with the shooting. It is currently unknown if there was a single shooter or multiple shooters involved," Oakland police said in a statement released around 1:30 a.m. Thursday.
Following the shooting, police said officers tried to guide the crowd into a safe area but some individuals in the crowd punched and pushed officers, resulting in minor injuries.
"One person was taken into custody for assaulting an officer," police said.
According to Oakland police, the Juneteenth-related celebrations in the area were not sanctioned gatherings.
The public is asked to avoid the area of I-580 at Grand Avenue.
Bay City News contributed to this story.