The New York explosion injured 29 people and was caused by one of two devices discovered in the city last night.
Republican Presidential candidate Trump, who hails from New York, jumped on the issue of national security as he appeared at an election campaign event in Colorado.
Mr Trump told supporters: ”Just before I got off the plane, a bomb went off in New York, and nobody knows exactly what’s going on.”
He continued: “We’d better get very tough, folks.
“It’s a terrible thing what’s going on in our world, what’s going on in our country.
“But we are going to get tough and smart and vigilant and we are going to end it.”
Democrat rival Hillary Clinton refused to say anything other than that she had been briefed.
Mr Trump’s remarks came several hours before New York officials publicly confirmed details of the incident or what caused the explosion, in Manhattan’s bustling Chelsea district, although it was later confirmed