A loose wheel flew off a car on the Grand Central Parkway Friday — then jumped the median and smashed into another vehicle, nearly killing one of the passengers, authorities said.

The wheel came off the driver’s side of a Mazda traveling west near the Cross Island Parkway shortly before 2 p.m.

It then bounced into the eastbound lanes and slammed into the passenger-side windshield of a Toyota RAV4, police said.

A 63-year-old man inside the Toyota suffered head trauma and was in critical condition. A 62-year-old who was also in the car suffered a shoulder injury, according to cops. Both men were taken to North Shore University Hospital in Manhasset, LI.

The driver of the Mazda, a 27-year-old woman, was also taken to the hospital along with her 15-month-old daughter.

They did not appear to be injured, police said.

The incident snarled traffic into the height of rush hour, as only one eastbound lane remained open.