Police are investigating a robbery in Brooklyn after a construction worker was shot on the job.

Police say the 21-year-old male victim was working at a construction site around 11 a.m. Monday near Belmont Avenue and Shepherd Avenue.

According to authorities, the robber knocked the victim down while trying to steal his gold chain.

After a struggle, cops say the man fired several shots, striking the victim twice in the abdomen and once in the elbow.

We spoke with a woman who was there.

"When I saw him bleeding there, I just had to do something," the witness said. "So, another bystander came along and applied pressure to the other side of the wound until EMS came."

Police say the suspect fled in a dark-colored Suburban.

The victim was taken to Brookdale University Hospital in serious condition.

Anyone with information on the case should contact the Crime Stoppers hotline at 1-800-577-TIPS, or text CRIMES and then enter TIP577, or visit www.nypdcrimestoppers.com.