Two masked gunmen are reported to have opened fire and released teargas in a crowded cinema in the town of Aurora, Colorado in the US.
Police are reported to have arrested one of the men, who was caught with a number of high calibre weapons. His accomplice is believed to be on the run.
TV host and journalist Piers Morgan reacted with outrage to the shocking incident:
"Horrendous details from this Colorado cinema shooting. America has got to do something about its gun laws. Now is the time," he posted as @piersmorgan.
He followed this up with: "More Americans will buy guns after this, to defend themselves, and so the dangerous spiral descends. When/how does it stop?", which sparked a wave of criticism from the CNN host's followers.
The Avengers' Captain America @ChrisEvans woke up to news of the shooting: "what the hell is happening?? my heart is completely shattered. all of my thoughts and prayers are with the people of aurora."
Rihanna reacted with shock on Twitter as news of the shooting broke, replying to one of her fans:
"@DontBeTheReason: Praying for all those people that died or were injured at the Dark Night Rises Premier. Rest in Peace." what happened?!— Rihanna (@rihanna) July 20, 2012
Comedian and Think Like a Man star Kevin Hart @KevinHart4real wrote: "just heard about the Shooting n Denver @ the movie theater, my prayers go out 2 the family members of the victims of this terrible tragedy (sic)"
Actor @JohnLeguizamo was also concerned about the gun laws in the US: "My heart goes 2 all the victims families in colorado. No one should have to go thru that. When r we gonna get guns removed in this country?! (sic)"
"Praying for the people of Aurora, Colorado," wrote hip-hop mogul Russell Simmons, tweeting as @UncleRUSH.
"Such awful, awful news this morning. All those people. It's so, so important we take care of each other. Thinking of the people of Denver," wrote Raising Hope actress @MarthaPlimpton.
South African singer Chris Chameleon @chrischameleon wrote: "a very bad side effect of the denver shooting is the subsequent pressure to change gun laws. i believe in a well armed population."
The Lord of the Rings star Dominic Monaghan (as @DomsWildThings) wrote: "Denver you are in our thoughts."
His words were echoed by Shaun of the Dead director @edgarwright.
US President Barack Obama and First Lady Michelle Obama also voiced their support for the victims of the tragedy.
The Dark Knight Rises opened in the US on Friday, and releases in the South Africa on 27 July.