At least 14 people have been killed and 50 injured in a shooting at a cinema near the US city of Denver, police say.
A man wearing a gas mask opened fire after tossing a tear gas canister at a midnight showing of the new Batman film, The Dark Knight Rises, in Aurora.
A 24-year-old man was arrested in a car park nearby in possession of a rifle and handgun. One other gun was recovered from the theatre.
The suspect told police that explosives had been stored at his home.
Police chief Dan Oates told reporters that an apartment block in the north of Aurora had been evacuated as they investigated that information.
‘No terrorism link’
US President Barack Obama has spoken of his shock at the incident, which began at about 00:30 local time (06:30 GMT) at the Century 16 cinema complex.
Mr Oates told a news conference the shooting was “a horrific event”.
“Witnesses tell us he released some sort of canister,” he added. “They heard a hissing sound and some gas emerged and the gunman opened fire.”
“The shooting apparently went on for some time.”
Ten people were killed at the cinema and four others died later in hospital of their wounds, he said.
The FBI, which is working with the police, says no terrorism link has been established.
Many ambulances attended the scene. Officials at the Swedish Medical Center, not the area’s main hospital, told the BBC the facility had received several gunshot victims and expected more.
Local media report that six victims, ranging in age from six to 31, were being treated at the Aurora Children’s Hospital.
One witness said a man in a bullet-proof vest and riot helmet had been “slowly making his way up the stairs and just firing – picking random people”.
Another witness, Chayyiel Jackson, told the BBC: “During the first action scene in the movie, on the right side a dude came in all blacked out, with a black mask. At first we thought it was part of the movie event.
“He threw tear gas across the crowd and after that people started to panic. He pulled out a rifle and started shooting.
“I was wondering if this was real life or a dream.”
Hospital officials said some of the wounded were being treated for the effects of tear gas.
Another eyewitness, identified only as Pam, told the BBC: “He fired a canister into the air. It shot it right into the air, then I started to hear the bang, bang, bang of a gun.
“I crawled my way through the row. Luckily the exit was close to where I was sitting so I got out pretty fast. I heard more shots as I left.”
Another eyewitness, Salina Jordan, 19, told the Denver Post she had seen one girl shot in the cheek, and a girl who appeared to be about nine years old with a gunshot wound to the stomach.
A witness in the next-door theatre told 9News he initially thought live special effects had been laid on by the cinema after hearing loud bangs and seeing smoke.
President Obama said in a statement that he and First Lady Michelle Obama were “shocked and saddened by the horrific and tragic shooting in Colorado”.
He added: “We are committed to bringing whoever was responsible to justice, ensuring the safety of our people, and caring for those who have been wounded.
“As we do when confronted by moments of darkness and challenge, we must now come together as one American family.”