Cops shot a chain-wielding mad man in East Harlem tonight after he went berzerk and swung a 4-foot-long metal chain at an officer, police said.

The officers were responding to a call of a crazed man swatting pedestrians with a chain on 3rd Avenue and East 103rd street at around 8 p.m.

An officer ordered the suspect to put down the chain and the man refused, cops said.

The suspect then took a swing at the officer who shot him once in the stomach.

He was taken to St. Luke’s Hospital in Manhattan and listed in critical condition last night.