A crazed gunman shot dead a three-month-old baby as horrified police looked on during an armed standoff in upstate New York Tuesday, WKTV reported.

State troopers spotted the man outside a house in Blossvale, N.Y., after racing to the scene of a domestic dispute.

He shot the baby dead and then opened fire on the officers, WKTV said.

Officers fired back, injuring the gunman but not fatally. The baby was rushed to the hospital but was pronounced dead.

Two more young children were inside the house when the gunman began shooting at 9.30am local time but they were both unharmed, police said.

Officers have not revealed the names and relationships of those involved.