The 22-year-old singer was signing autographs for fans when someone opened fire, according to reports.
Christina’s brother tackled the man, who then shot himself, while Christina was initially rushed to hospital.
The sad news was confirmed on Twitter by the Orlando police, who wrote:
They also detailed how the incident took place:
A statement from Christina’s publicist, issued to E! News, reads: “It is with a heavy heart that we can confirm that Christina has passed and went home to be with the Lord.
"She was shot at her show in Orlando and, unfortunately, didn't survive the gun shot wounds.
"We ask at this time that you respect the privacy of her family and friends in their time of mourning.
"If you'd like to give back to Christina's family in her memory, please consider donating to the family's GoFundMe page in their time of need."
TV and music fans will recognised Christina from the 2014 series of the talent show, in which she came third.
During the show’s blind auditions, Christina’s tremendous vocals led to all four coaches turning their chairs around, and the hopeful ended up being on Adam Levine’s team.