MIAMI (REUTERS) - Christina Grimmie, a rising singing star who gained fame as a YouTube sensation and contestant on television's The Voice, died after being shot while signing autographs at a concert hall in Orlando, police said on Saturday.

The suspected attacker died of a self-inflicted gunshot wound after he was tackled by the 22-year-old singer's brother, police said.

Authorities believe the suspect, identified only as a 21-year-old white man, had travelled to the Florida city specifically to carry out the attack on Friday evening, though there was still no apparent motive for the shooting.

Orlando police chief John Mine told reporters the suspect did not appear to have a criminal record and there was no indication he and Grimmie knew each other.

Mine said it appeared he may have been a deranged fan.

"That'd be speculation, but that's what it's looking like. We believe he came here to commit this crime," Mine said when asked about the possibility.

Detectives will search the suspect's home, cell phone and computer before releasing further information, he added.

Grimmie was signing autographs for fans inside the Plaza Live concert hall at the time of the shooting, around 10.30pm (10.30am Singapore time). She had just appeared as the opening act for the band Before You Exit.

The suspect, who was armed with two small-calibre handguns and a hunting knife, approached Grimmie and opened fire before being tackled by the singer's brother, an act that police said probably saved lives.

Grimmie was taken to a local hospital in critical condition and died early Saturday morning. The suspect died at the scene of the shooting.

Although patrons had their bags and purses checked for weapons at the venue, there were no metal detectors and the security guards were unarmed, Mine said.

'BEAUTIFUL SOUL'

The attack, the latest high-profile shooting to rock the country, drew a quick response from anti-gun activists.

"While the details of this shooting are still being investigated, one thing we already know is that there is so much more Florida policymakers can do to prevent gun violence and keep guns out of dangerous hands," said Dan Gross, the president of the Brady Campaign to Prevent Gun Violence.

A New Jersey native, Grimmie first gained attention several years ago for her YouTube videos featuring covers of pop songs, which drew millions of views. In 2014, she placed third on the The Voice, a singing competition broadcast on NBC.

Fans took to social media to express their sorrow, with the hashtag #RIPChristina trending on Twitter.

"There are no words," tweeted The Voice early on Saturday. "We lost a beautiful soul with an amazing voice."

Josh Kaufman, who beat out Grimmie to win the 2014 season of The Voice, tweeted, "My deepest and most sincere condolences go out to the family of @TheRealGrimmie. Such a tragic loss."

Grimmie's own Twitter account still showed a video she posted on Friday asking fans to come out to see her perform.

Her account tweeted a simple message on Saturday morning: "The end."

However, a report on the People website quoted Grimmie's representatives as saying that the star's Twitter account had been hacked.

The post was retweeted more than 65,000 times within an hour.