A shooting incident at the Great Mall was first recorded on Saturday at 5:23 p.m. local time, according to ABC 7.
The Santa Clara County sheriff's office tweeted that sheriff's deputies are on scene assisting Milpitas police.
Police have asked the public to avoid the area while officers are investigating the shooting incident. All shops at the Great Mall are urged to shelter-in-place.
It is unclear whether there are any casualties or damage, nor it is known if there is an active shooter on site.
ABC 7 said that one witness shared videos from a Guess store inside the mall, adding that there were 40 people inside with her. All were reportedly told to lock themselves inside.
Another user posted a video, saying they were stuck inside the Colombia stock room due to the shooting incident.
Other videos allegedly taken at the scene show a heavy police presence around the mall.
No further details are immediately available.