At least 17 people have been injured in a mass shooting on a New York subway overnight.

A gunman in a construction vest and gas mask set off a smoke canister on a rush-hour train in Brooklyn before opening fire.

He then fled the station as commuters ran for their lives.

US Correspondent Harley Carnes told Spencer Howson tracking the gunman could be near impossible for investigators.

“When the doors of the subway opened, the first thing that came out was smoke and a lot of it,” he said.

“And then people in a panic and he could have easily got himself lost in that crowd, which he did.”

Press PLAY below to hear Harley Carnes’ full report 

Image: Will B. Wylde / Twitter