CONTENT WARNING: This article contains footage that some readers may find disturbing or distressing.

New Yorkers are sharing horrifying footage online after a mass shooting on a Brooklyn subway train.

New York Police identified the shooter as Frank R. James on Tuesday night, local time. His keys were found at the scene. Police also found a rental car six kilometres from the subway that they say may have been used by him.

At the time of writing, there have been no deaths linked to the Tuesday morning attack.

Five people are in critical condition but are expected to recover. At least 29 others were hospitalised for smoke inhalation, gunshot wounds and other conditions.

Per the New York Times, the Brooklyn subway shooter was masked and in a construction vest when he approached the Brooklyn train. He reportedly let off multiple smoke bombs and opened fire.

“My subway door opened into calamity. It was smoke and blood and people screaming,” witness to the shooting Sam Carcamo told New York radio station 1010 WINS.

“There was a lot of loud pops, and there was smoke in the other car,” witness Juliana Fonda, who was reportedly in a neighbouring train carriage, told Gothamist.

“And people were trying to get in and they couldn’t, they were pounding on the door to get into our car.”

“I saw a lady, she was shot right in her leg and she was screaming for help,” witness Yayha Ibrahim told Reuters.

“[Rescue workers] did a good job of coming quick and fast, and the ambulance came in and they took her.”

New York Police announced a US$50,000 reward for anyone who provides information that could lead to the arrest of the shooter.