Brooklyn shooting: police search for suspect after more than 20 injured

Authorities identify person of interest in subway attack as Biden says we're not letting up until we find the perpetrator'

• Brooklyn shooting - latest updates

A gunman wearing a gas mask filled a crowded New York subway car with thick black smoke from a canister and opened fire on morning rush-hour passengers, injuring more than 20, including 10 with gunshot wounds.

A manhunt was under way on Tuesday after the shooter fled the scene. A 9mm semi-automatic handgun and extended magazines, a hatchet, a black garbage can, detonated and undetonated smoke grenades and a key to a U-Haul van were also found at the scene, authorities said. Officers located the vehicle, which will be examined by a bomb squad.