A Friday morning screening of the new Batman movie turned from entertainment to horror in the US city of Denver, after a shooting spree killed at least 12 people and wounded 40 others including a 3-month-old baby, according to witnesses.

The shooter was identified as 24-year-old James Holmes, according to NBC. Holmes has been taken into police custody, local police chief Dan Oates told reporters, without elaborating on the motive of the shooting in the Denver suburb of Aurora.

US President Barack Obama said he was "shocked and saddened" by the mass shooting 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," Obama said. "We are committed to bringing whoever was responsible to justice, ensuring the safety of our people, and caring for those who have been wounded."

He also cut his reelection campaign trip short after the shooting spree.

Witnesses 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 theater with bullets, AFP reported.

Police arrested the suspect in the parking lot behind the theater, police spokesman Frank Fania told Reuters.

"He did not resist, he did not put up a fight," he said. The suspect's apartment building has been evacuated after the suspect spoke of a possible explosive in his residence.

"At this time, the police have no evidence that any additional suspects were involved other than the person arrested," the Aurora police said in a statement.

A spokeswoman for Denver's Swedish Medical Center said three people had been admitted to that hospital with gunshot wounds and were in a critical condition.

Another hospital, Denver Health, had received six wounded, one of whom was in a critical condition, spokeswoman Kalena Wilkinson said.

New York has announced to step up its security measures after the bloodshed.

"As a precaution against copycats and to raise the comfort levels among movie patrons in the wake of the horrendous shooting in Colorado, the New York City Police Department is providing coverage at theaters where the movie is playing in the five boroughs," police chief Raymond Kelly said in a statement.

Jessica Ghawi, an aspiring sportswriter who had been in a Toronto mall just ahead of a shooting spree, was reportedly among the victims of Friday's rampage in Denver.

KENS-TV reported her death, quoting family members in Texas.

Ghawi, whose killing prompted an outpouring of grief and sympathy from friends and colleagues, was tweeting just moments before she was shot.

"Movie doesn't start for 20 minutes," she wrote just ahead of the shooting early Friday in Denver.

KENS-TV said Ghawi recently moved to Denver from San Antonio to pursue her career.

Shi Yinhong, director of the Center of American Studies at Renmin University, told the Global Times that the US' culture of guns was to blame in part for the tragedy.

"As long as you don't have a criminal record, you're allowed to own a gun in the US. Crimes involving firearms are not unique to the US, but the gun crime rate in the US is far from the lowest [in the world]," Shi said.

The attack on moviegoers took place just a few kilometers from the scene of one of the most notorious shooting sprees in US history at Columbine High School in Littleton, another suburb of Denver. Teenagers Eric Harris and Dylan Klebold carried out the massacre in 1999, killing 12 students and a teacher before taking their own lives.

Seventeen people were hurt on Tuesday after a gunman fired into a crowded bar in Tuscaloosa, Alabama, before shooting at people as they ran out.

Global Times - Agencies