A dump truck driver struck and killed a 21-year-old man in the Bronx Thursday — one of two hit-and-runs in the city Thursday morning.

Ronald Nival was crossing the Cross Bronx Expressway sometime before 2:30 a.m. when he was hit by a 2013 Peterbilt Dump Truck driving east in the center lane, according to police.

Cops found Nival unresponsive on the side of the road in Soundview, where he died.

The dump truck did not stop, but police tracked down the driver, who said he did not notice he had hit someone.

No one has been charged in the man’s death, and the crash remains under investigation.

A second hit-and-run happened about four hours later in East Harlem, where the driver of a Nissan Altima barreled into a 33-year-old woman crossing the street, cops said.

That driver didn’t stop either — but a short time later, the 27-year-old driver walked into a nearby precinct to report the accident, according to police.

No charges have yet to be filed against her.