Grandfather killed in hit-run outside Melbourne primary school

A grandfather was killed in a hit-and-run in front of a primary school in Melbourne's south-east.

Police are questioning how a driver left a 73-year-old man on the side of the road after he was struck while going for a morning walk in Hampton Park this morning.

"What goes through the mind of a driver when they've run a person over to leave them there, you wouldn't do it to a dog," detective sergeant Mark Amos said.

"Why would you do it to a person?"

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The hit-and-run happened about 5.20am, with a crime scene established outside Kilberry Valley Primary School.

Students and parents were redirected away from the area as they arrived for school drop-off.

Police are working to track down the driver and determine exactly what happened.

Officers are combing through CCTV footage of the area.