Washington - US President Barack Obama said he was "shocked and saddened" by the mass shooting at a Denver-area cinema early on Friday in which at least 12 people were killed and 50 wounded.
"Michelle and I are shocked and saddened by the horrific and tragic shooting in Colorado," he said in a statement, adding that federal and local law enforcement were still responding to the incident.
"My administration will do everything that we can to support the people of Aurora in this extraordinarily difficult time," he said, referring to the city adjacent to Denver where the shooting took place.
"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."
Obama was notified of the mass shooting at 05:26 by his homeland security advisor John Brennan, according to White House spokesperson Jay Carney. The president is currently in Palm Beach, Florida.
Witnesses had described a scene of chaos as the gunman burst into a packed showing of The Dark Knight Rises, the latest Batman film, setting off a smoke device of some kind and spraying the theatre with bullets.
The youngest victim is reportedly a 3-month-old baby.
Chris Jones, who was in the theatre, said the shooting began about 20 to 30 minutes into the screening.
"People just started dropping. We were on the floor trying not to get shot," Jones told the local KMGH-TV television station.
"I thought it was just fireworks. There was smoke, then I heard 'bam, bam, bam'. The gunman didn't have to stop to reload. Shots just kept coming, kept coming, kept coming."
Police have detained the alleged gunman, who is said to be 24-years-old, but have released few details about his identity or motives.
9news reported that the suspect, after being captured by police, told authorities he had explosive materials in his apartment.
According to the Colorado-based station said police went to his apartment building at East 17th Avenue and Peoria Street in Aurora and evacuated the building immediately as a precautionary measure.
Police are searching his apartment to confirm that claim, it said.