The robbery happened at 8:50 a.m. Friday at the Chase Bank on Warburton Avenue.
The man displayed an assault rifle and a handgun to the teller and bank manager and told them to get on the floor.
However, the victims say the suspect remained calm and polite.
He got away with several thousand dollars and fled the bank on foot.
The suspect is described as a black male in his late 20's, approximately 5'9"-6' tall.
The individual was wearing a green camouflage jacket with a hood, orange goggles, black pants, and black gloves.
"This is a very dangerous situation; although this subjects' face is hidden from view, we know someone out there may have information that could lead to his arrest. He needs to be caught right away. The FBI's Westchester County Violent Crimes Task Force and the Hastings-on-Hudson Police Department will continue to investigate this incident until the subject is located and brought to justice. Please contact the FBI at 212-384-1000, the Westchester County Police Department at 914-864-7832, the Hastings-on-Hudson Police Department at 914-478-2344, or your local police if you have any information that could assist with his apprehension. A cash reward is available for information leading to the arrest of this individual; anyone who submits a tip may remain anonymous," said Supervisory Special Agent Richard Kolko.