A man has given a graphic account to the FBI of the New York terror attack, saying the suspect came within metres of him, "eyeballing" him as he waved guns in the air, and spoke incoherently.

"He gets out of his pick-up truck and he's coming towards me," Anthony, who was waiting outside a primary school in lower Manhattan for his 12-year-old son, told Fairfax Media on Wednesday.

"He had a big thick beard, very long, and he was expressionless."

"He was talking to himself out loud, not really screaming. It was gibberish. He could have been saying: God is great in Arabic. I couldn't understand it."