First details about the gunman who reportedly opened fire in a Colorado theatre, killing 12 and wounding at least 50 others, have emerged.

Police have arrested a suspect who is apparently aged 24 and who told officers he had explosives in his car and home.

Witnesses described who a man opened fire at a midnight screening of The Dark Knight in Aurora after throwing tear gas into the crowds.

The gunman was reportedly wearing a "Bane-style" gas mask, body armour and carrying one rifle and two handguns in the Aurora, Colorado cinema complex.

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Police searched a Hyundai in the complex car park, after the man claimed he was in possession of explosives

After the man told police he was in possession of explosives, a police bomb squad began examining a Hyundai in the cinema's car park for an explosive device, while the man's apartment block was evacuated and searched for further evidence.

"The suspect who is in custody made a reference to explosives at his residence, so police have evacuated a building in North Aurora," Aurora police chief Dan Oates told the media.

"It's an apartment building, that we have evacuated and we are dealing with the potential that there are explosives inside there.

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Police evacuated and searched the man's apartment block for explosives

"We have all the area bomb squads close at hand and we are just as a precaution checking all the bars and the parking lots for explosives."

You can watch video of cinema-goers fleeing the cinema as the shootings occurred below.

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