New York City police shot and killed a hatchet-wielding man on Thursday after he suddenly attacked a group of patrol officers without warning in broad daylight on a busy commercial district in Queens.

At a news conference at a hospital where one officer was being treated for a serious head wound, Police Commissioner William Bratton said that investigators were still trying to confirm the identity of the assailant and determine a motive.

Security videotape and witness accounts appeared to leave no doubt that the man purposely targeted four rookie New York Police Department officers, police said. Moments before the attack, he was seen on a street corner crouching down to pull the hatchet out of backpack before he charged the officers and began swinging the hatchet with a two-handed grip, police said.

Asked if the attack could be related to terrorism, Bratton didn't rule it out. He cited the fatal shooting of a soldier in Canada earlier this week — what officials there have called a terror attack — as reason for concern.

"This early on, we really cannot say yes or no to that question," Bratton said.

The attack occurred at about 2 p.m. while the officers were standing together on foot patrol, police said. Without a word, the man swung at an officer who blocked the blow with his arm. Another officer was hit in the back of the head and fell to the ground.

As the man raised the hatchet again, the two uninjured officers drew their weapons and fired several rounds, police said. The bullets killed the assailant and wounded a female bystander, police said.

The officer was in critical but stable condition and was expected to undergo surgery. The woman who was struck by a stray bullet also was hospitalized with a gunshot wound to the back.