‍A woman opened fire at YouTube's headquarters in Northern California on Tuesday has practiced shooting hours before the attack, according to police.

San Bruno Police Chief Ed Barberini said after practice, the female brought a Smith & Wesson 9mm semiautomatic handgun to the Silicon Valley campus, where she shot and wounded three strangers.

 Two of the victims were discharged from hospital and one remains in critical condition.

The suspect, identified as Nasim Aghdam later killed herself.

What's the motive?

Local police believed anger with Youtube's policy leads to Tuesday's shooting.

"We know she was upset with YouTube, and now we've determined that was the motive," Barberini said.

Police officers are seen at YouTube headquarters after a woman opened fire in San Bruno, California, US, April 3, 2018. /VCG photo

The 39-year-old woman had previously claimed in a video that YouTube "discriminated and filtered" her content before her channel was deleted on Tuesday.

"Whether that rises to the level of terrorism hopefully will be determined in the next couple of weeks," Barberini added.

What had happened?

The shooting took place at around 12:48 p.m. in an outdoor cafe at the YouTube campus which houses some 1,700 employees.

Officers later arrived to find a "chaotic scene", with numerous people fleeing, according to Barberini.

During the shooting, Aghdam was heard in the courtyard yelling, " 'Come at me,' or 'come get me!' " according to CNN, citing a YouTube staff.

After opening fire at strangers, Aghdam's was found dead inside the complex of "self-inflicted wound".

YouTube headquarters in San Bruno, California, US. /AFP Photo

Who's the suspect? 

Aghdam has been blogging about surviving in a world filled with “injustice and diseases”, covering various subjects including animal cruelty and vegan lifestyle.

Her YouTube channel has now been deleted. Her Instagram and Facebook accounts have also been removed.

Aghdam has long criticized YouTube for filtering her content and limiting views.

According to multiple media reports, Aghdam used to rant on the company on her personal website saying, "There is no equal growth opportunity on YouTube or any other video sharing site. Your channel will grow if they want [it] to!"