A man was struck and killed by a train in Brooklyn early Sunday when he jumped onto the tracks to retrieve what authorities believe was a cell phone.

The southbound Q-train operator, rolling into the Prospect Park station on Flatbush Avenue shortly after 3 a.m., saw the victim hop onto the tracks to pick something up, law enforcement sources said.

But the operator wasn’t able to stop the train in time and the man, whose identity was not immediately known, was crushed between the platform and train, authorities said.

The man was pronounced dead at the scene.