Boy dies, girl critical after being stabbed in New York lift

New York City police are searching for a man who stabbed and killed a six-year-old boy and critically wounded a seven-year-old girl as they took a lift up to a Brooklyn apartment to get ice cream.

Police flooded Brooklyn's East New York neighbourhood with extra officers to assist in the manhunt and reassure frightened residents.

Police described the attacker as a stranger who chose the victims randomly.

"This is particularly heinous crime," Police Commissioner William Bratton said. "Two young children in an elevator with no place to escape, and some character gets on and starts stabbing them? People have every right to be concerned."

Before the attack at 6pm on Sunday, the children had been playing together outside a city housing project under adult supervision. They went inside alone to get some ice cream from the boy's sixth-floor apartment when they were cornered by a heavyset man in his 20s. The man used a steak knife to stab each child multiple times. He fled on foot, leaving behind the knife.