The hashtag #guncontrol began trending on Twitter immediately after gunmen opened fire at a disability centre in San Bernardino, California earlier today.
At least 14 people are dead and 17 injured after the shooting.
The hashtag #guncontrol became the fourth highest trending topic on Twitter in New Zealand for an hour in the shooting's immediate aftermath.
Democratic presidential candidate Hillary Clinton tweeted in support of gun control.
Entertainment correspondent Jessica Radloff also encouraged her 11,000 followers to demand better gun control.
Twitter user Scotty, from Auckland, said: "Day 336 of the year in the USA, and yet another mass shooting ongoing. This is the 352nd of the year! #guncontrol #statsdontlie..."
Another Auckland tweeter, Neville, wrote: "Just reading about the awful #SanBernardinoshooting. A centre for disabled children?! Jesus Christ America, this is a new low! #guncontrol..."
Neville then tweeted an image of a 2015 calendar featuring the dates of US mass shootings. Alongside it he wrote: "Quick reminder as to the scale of the problem of mass shootings in the US. Beyond belief. #guncontrol..."
Meanwhile, Donald Trump, Republican presidential candidate, said: "California shooting looks very bad. Good luck to law enforcement and God bless. This is when our police are so appreciated!"
The #guncontrol hashtag went viral on Twitter in the US.
A woman named Ashley Hughes tweeted: "How many America? How many shootings does it take to establish effective #guncontrol? I'll be back in the EU until you can answer."
Grant Harvey wrote: "Even if #GunControl didn't work (It would work), we would at the VERY LEAST be making an attempt to stop this ceaseless violence. @POTUS..."
Rachel Palmer tweeted: "I just assume in everyday interactions that everyone has a gun. I feel less secure in the US than anyplace I've lived globally. #guncontrol..."
The hashtag #SanBernardino was the number one trending topic on Twitter in New Zealand and worldwide.
Actually, #SanBernadino was - the world having some issues with spelling the Californian city correctly.