For those of you who haven't seen City on Fire, here's a synopsis. It's pretty much Reservoir Dogs in plot:
In 1987, Hong Kong director Ringo (Full Contact) Lam made a film called City On Fire, starring Chow Yun-Fat as a heavily conflicted cop who goes undercover with a gang of thieves who plan to rob a jewelry exchange. Members are strictly forbidden to swap names or backgrounds, but Chow is befriended by career criminal Danny Lee, and suffers pangs of guilt over the fact that "doing his job" will mean betraying him.
The heist goes sour when another thief starts shooting hostages, and the cops appear out of nowhere. Chow, wounded in the stomach, reflexively kills his attacker -- a cop -- and is rescued by Lee, who stands in the path of an oncoming police truck, gun in either hand, and calmly riddles its occupants with bullets. After taking refuge in a deserted warehouse, the gang's boss decides there's a police informant among them: Chow. Lee comes to his buddy's defense, triggering a three-way stand-off that ends in a hail of bullets. As Lee holds the dying Chow in his arms, Chow tearfully admits he's a cop, then waits for Lee to finish him off.