Building burns in Cairo clashes

(ROUGH CUT ONLY - NO REPORTER NARRATION)
Black smoke billows from a six-storey apartment building near Tahrir Square, as clashes flare between demonstrators and security forces.
Firefighters arrive at the scene, but police fire tear gas canisters from a side street, angering bystanders.
A witness claims that the fire was started by a stray tear gas canister.
A woman screams for help from the top floor, and some residents try to scale the building to rescue those trapped.