It happened early on Sunday morning at a private party in San Jose's Fiesta nightclub, near San Francisco.
Police have confirmed the Grammy winner was unhurt.
Mobile phone footage said to be of the gig has been posted online and shots can be heard in the middle of one of Brown's songs.
In a video, posted on his own Vine profile, he can be seen looking at something going on in the crowd before shots ring out.
He appears to be wincing, before security guards escort him away.
Other footage posted online shows the aftermath of the shooting.
There appear to be a few hundred people in the crowd, and most of them run for the exits or drop to the ground. Many are crying or screaming.
The San Jose Police Department says all five people injured in the shootings are expected to survive.
It says it is still investigating the "motive surrounding the shootings" and "several people have been detained by officers".
The singer has made no public comment on the shooting.
According to the newspaper the San Jose Mercury News, shortly afterwards he tweeted "I'm 100" to tell fans he was uninjured, but that tweet was later deleted.
It's not the first shooting incident Chris Brown has experienced.
In August last year the singer was hosting a party in Los Angeles when Death Row Records executive Suge Knight was shot.
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Jessica Taylor suffers debilitating fatigue and painful muscles caused by Chronic Fatigue Syndrome, also known as Myalgic Encephalomyelitis (ME).
The 25-year-old, of Cliffe Woods, Kent, met Samuel Bearman, 24, through friends and they plan to marry next year.
She is working with a physiotherapist in her bid to walk again, and said the wedding would be a "dream come true".
"I've tried to defy doctors. They've given me boundaries and I've tried to extend those boundaries as much as possible," she said.
Mr Bearman said his fiancee was much more than just "someone stuck in a bed".
Ms Taylor added: "There's still a life you can live and it's not wasted years."
Two years ago, with her sister Ruby, Ms Taylor started a charity called Share a Star, which supports sick children who spend their lives indoors.
Last month she was invited to the Houses of Parliament to talk to her local MP, Kelly Tolhurst, about its work.

Imaginative thinking would be required to ensure trade between Northern Ireland and the Republic of Ireland was not affected, said Mr Ahern.
But he believed customs checks were inevitable.
Mr Ahern added that now was not the time for a border poll.
Speaking to the BBC's Today Programme, he said: "There has to be far more consensus, there still is a divided society, the institutions are not operational.
"The big issue, I think, for the Irish and the UK government is on the other side of 8 June is to try to help broker a deal to get the institutions back up and running and certainly having a border poll in the foreseeable future will not help that process."
In March, Mr Ahern told the BBC's Newsnight programme that dissident republicans might use the re-introduction of border posts in Northern Ireland to justify their campaign of violence.
He said a hard border with customs checks would have to be re-introduced because of the UK's decision to leave most of the customs union under Brexit.
Mr Ahern drew a comparison with the IRA's so-called Border Campaign in the 1950s.
But he said he did not expect a return to large-scale violence.
The UK government has pledged to ensure there will be no return to the "hard border" of the past.
Five people have been shot at a California nightclub while Chris Brown was performing.
[NEXT_CONCEPT]
A woman is planning to walk down the aisle on her wedding day despite being bed-ridden for almost half her life.
[NEXT_CONCEPT]
Former Taoiseach (Irish prime minister) Bertie Ahern has warned there is no easy solution to resolving the Irish border issue before the UK leaves the EU.