At least 14 people have been killed - and around 50 injured - after a gunman opened fire during a midnight screening of the latest Batman film in the US.

Witnesses say a gunman walked in to a shopping mall in Denver, Colorado wearing body armour and a gas mask, before setting off tear gas - and some initially thought it was a publicity stunt.

A man's been arrested and police are now searching his apartment for explosives. 

Dan Oates from the local Police Department says he's only aware of one gunman, despite earlier reports that there might have been two: