A tanker truck fatally struck a cyclist in Brooklyn on Thursday night — and then left the scene, police said.

The cyclist was riding near Marcy Avenue and Broadway in Williamsburg when the truck smashed into her at about 11:35 p.m., cops said.

The truck driver did not stop, possibly because he did not realize he had struck the 25-year-old cyclist, police said.

Police are investigating the crash. The cyclist’s name was not released.