A man tried to rob a bus full of people on the Upper East Side on Tuesday morning but made off without any cash, police said.

The suspect, in his 20s and about 6 feet tall, got on the M4 bus at 110th Street and Fifth Avenue just before 8:50 a.m., police said.

He demanded cash from the 10 or so passengers before making his way to the front of the bus. He then took out his knife and demanded money from the 32-year-old bus driver.

Police finally met up with the bus by 81st Street and Fifth Avenue, but the suspect had gotten off at some point and ran off without any money.