A gunman in a construction vest donned a gas mask, set off a smoke canister on a New York City rush-hour subway train and shot at least 10 people Tuesday morning, authorities said. The shooter was at large and described as dangerous after leaving wounded commuters bleeding on a Brooklyn platform while others ran screaming.

Five people were in critical condition but expected to survive. At least 16 in all were injured in some way in the attack that began on a subway train that pulled into the 36th Street station in the borough’s Sunset Park neighbourhood.

Police Commissioner Keechant Sewell said that the attack was not being investigated as “terrorism”, but that she was “not ruling out anything”. The shooter has not been identified and the motive remains unknown.

“My subway door opened into calamity. It was smoke and blood and people screaming,” eyewitness Sam Carcamo told radio station 1010 WINS, saying he saw a giant billow of smoke pouring out of the N train once the door opened.

The attack unnerved a city on guard about a rise in gun violence and the ever-present threat of attacks. The shooting left some New Yorkers jittery about riding the nation’s busiest subway system and prompted officials to increase policing at transportation hubs from Philadelphia to Connecticut.

The incident happened on a subway line that runs through south Brooklyn in a neighbourhood predominantly home to Hispanic and Asian communities and about a 15-minute train ride to Manhattan. Local schools, including Sunset Park High School across the street from the station, were locked down with students sheltering in place, as police hunted for the suspect.