A would-be Bronx crook flashed a knife at a 91-year-old man in broad daylight this week, cops said. 

The senior was walking at East 161st Street and Grand Concourse in Concourse Village around 3:30 p.m. Monday when a stranger approached him from behind, police said. 

The suspect flashed a knife and demanded money, authorities said. 

The nonagenarian immediately backed away, but fell and hit his head, cops said. 

He was rushed to Lincoln Medical Center, where he was listed in stable condition. 

Surveillance video released by the NYPD late Monday shows the still-at-large suspect walking away. 

In a separate incident in Brooklyn about two hours later, a hateful stranger approached a 77-year-old man on Broadway near Rutledge Street in Williamsburg, police said. 

He flung an open boxcutter at the senior’s face while snarling, “You f–king Jew!”, cops and police sources said. 

The victim was treated by EMS at the scene, and the alleged bigot took off, police said. 

Video released by the NYPD late Monday shows the suspect, who is also still on the loose, riding a motorcycle. 

The NYPD’s Hate Crime Task Foce is investigating the incident, police said.