A good Samaritan was killed Friday on the Verrazano Bridge when he was struck by the runaway car of an injured motorist he had stopped to help.

The bizarre chain-reaction accident happened about 12:30 p.m. after a 52-year-old man hopped out of his 1994 blue Ford van when it conked out on the span’s upper level.

As the driver was trying to repair his vehicle, a 2007 box truck slammed into the back of it, causing him to “be pushed forward, sustaining trauma to the body,” cops said.

The good Samaritan, a 70-year-old man, stopped his 2010 Nissan Rouge in the center lane and rushed to aid the injured man.

But the injured man’s van, after reportedly getting propelled farther up the bridge by the force of the first crash, suddenly rolled backward, striking the good Samaritan.

He was rushed to Lutheran Medical Center, but doctors could not save his life, police said.

The 52-year-old motorist who was injured was taken to Staten Island University Hospital North, where he was listed in critical condition, police said.

There were no arrests.