Aurora police chief Dan Oates told reporters that 10 people died at the scene and four others died after being taken to local hospitals. At least 50 other people were injured, Oates said.
One suspect was apprehended in the shopping center's parking lot, Oates said.
The incident occurred in the Century 16 Movie Theaters at the Aurora Town Center, police told NBC News. Aurora is a suburb less than 10 miles east of downtown Denver.
NBC station KUSA-Denver cited a witness as seeing a black-clad 6-foot-tall man wearing a riot helmet, goggles and bullet-proof vest. The witness and her boyfriend crawled to the emergency exit, KUSA said.
The suspect was found in possession of a gas mask and two firearms, Oates said. Ammunition was found in the suspect's car, police said.
At least 14 people were killed and dozens of others wounded early Friday in Aurora, Colorado after a gunman opened fire during a midnight screening of "The Dark Knight Rises" film. Willie Geist talks with KUSA's Jace LarsonThe police chief said there was no evidence of additional shooters.
The suspect's apartment building in north Aurora was evacuated after the suspect made a statement to police about possible explosives at his home, Oates said.
Witnesses told reporters that gunfire erupted during a shootout scene.
Brenda Stuart, of 850 KOA radio, told Sky News that "a lot of people thought the gunshots were part of the movie."
'I'm in shock'Tear gas also went off in the theater, Stuart said. She added that bullets had passed from one theater into an adjoining one.
One young man told KUSA that he was out front of the theater with friends when the shooting broke out.
"Next thing you know you hear 'boom' like tear gas, a bomb. ... Then you hear gunshots go off, like a fully automatic weapon. [There were] like 50-60 gunshots," he told KUSA.
"I was just worried about getting out of there," he told KUSA.
The man, who did not give his name, said he heard gunfire continue for at least 20 minutes.
"People were coming out of there screaming, some of the people were coming out of there bleeding. ... People were coming out with their shirts covered in blood," he said.
Another eyewitness, whose name was not given, told KUSA that he "saw at least 4, maybe 5 people limping, slightly wounded. ... I saw one girl covered in blood.
"I don’t know whose little girl that was, but my heart goes out to them. ... A cop came walking through the front door ... holding a little girl in his arms and she wasn't moving, she wasn't moving," the young man, whose voiced cracked as he spoke, told KUSA.
The Denver Post quoted witness, Bejamin Fernandez, 30, as saying that people ran from the theater as shots rang out.
Fernandez told the Post that he saw people falling, including one young girl.
Salina Jordan, 19, who was in Theater 8, told the Post she saw one girl struck in the cheek and others in the stomach, including a girl who looked to be around 9 years old.
Police officers converge at the scene of a mass shooting in Aurora, Colo., early Friday.
More on this story from breakingnews.com
Local emergency crews from several cities, including Denver and Boulder, converged on the scene, Stuart told Sky News.
Cathy Canzanora, a 911 dispatcher, told NBC News that emergency dispatchers were deluged with calls from "everybody who had cellphones in the theater" at 12:39 a.m. Friday local time (2:39 a.m. ET).
The dispatcher said she could not reveal what people told her but said that they reported "that there had been a shooting so we got the police and the fire department and the ambulance there as soon as they could."
Further local coverage from NBC station KUSA-Denver
Police cars transport the woundedThe injured were being transported to several local hospitals, police told NBC.
KOA's Stuart said that police officers were taking victims to hospitals in their cars and not waiting for ambulances.
Justin Bentzinger, a house supervisor at the Swedish Medical Center, told NBC News they were treating three patients. Two were in critical condition, the third was in fair condition.
Kalena Wilkinson, a public information officer for Denver Health, said six patients were taken to that hospital, with one in a critical condition and the other five in " fair" conditions.
Tracy Weise, of the public relations department at Aurora Medical Center, told NBC News they were treating 12 patients with a range of injuries from minor to critical.
"We have a variety of ages, quite a few 20s, teenagers, that kind of age," she said.
Jacque Montgomery, a spokesperson for University of Colorado Hospital, told NBC News that they were treating 20 patients from the shooting.
"Injuries range from minor to severe gunshot injuries," she said.
"The majority are adults. ... I know we have a handful of teenagers," Montgomery added.
Hundreds of witnesses who have not been injured have been taken to Gateway High School for a debriefing, local media reported.
"The Dark Knight Rises," starring Christian Bale and Anne Hathaway, is the latest in the popular Batman action movie franchise. Friday was its international premiere.