Brown had been performing for a few minutes when he noticed the commotion but was hustled offstage by his security entourage and was not injured.
It was not clear if the initial gunfire came from inside the Fiesta Nightclub and Restaurant at 3840 Monterey Highway, or if the first shots were fired in the crowded parking lot, according to the San Jose Mercury News.
But three gunshots that came later appeared to emanate from inside the bar, causing the crowd to flee in panic.
San Jose police said they found four people suffering from gunshot wounds when they arrived at the nightclub a few minutes after the shooting, and a fifth person later sought treatment at an area hospital.
“There was screaming, pushing and running,” Fiesta bartender Edgar Jimenez told the newspaper.
“Of course I was scared, because you’re in the middle of a shooting.” he said.
Police did not release names or injuries, but said all victims were expected to survive.
Several people were detained, police said.
The shooting began around 1:20 a.m., police said, as Brown was singing his hit song, “Loyal.”
The singer was at the nightclub for a VIP birthday event that included local DJs and commanded ticket prices as high as $2,500, the newspaper said.
Later that night, Brown tweeted a message to his 13.9 million Twitter followers of “I’m 100,” an apparent reference to him being 100 percent all right.
Many attendees posted cellphone video of the panic on social media.
The party had been scheduled for the Rockbar Theater on Saratoga Avenue but was moved at the last minute to the Fiesta because of crowd concerns.
The Fiesta usually features Mexican “banda” music, a genre featuring brass and percussion, but occasionally hosts rhythm-and-blues and hip-hop performers.
Brown, who is preparing to leave this month for a national tour, has been battling a long list of legal problems involving violent incidents with other singers, including a 2009 conviction for domestic violence after a run-in with Rihanna, his then-girlfriend.
