Trump made the statement before local officials had publicly confirmed details of the incident or what caused the explosion. Typically, national political figures use caution when describing unfolding situations and law enforcement actions.
"Just before I got off the plane, a bomb went off in New York and nobody knows exactly what's going on," Trump said at a campaign rally here.
Two hours after Trump spoke, New York City Mayor Bill de Blasio said the explosion "was an intentional act."
But, he said, "there is no evidence at this point of a terror connection." And the city's police commissioner, James O'Neill, said the "exact nature and cause" of the blast "has not yet been determined."
The Trump campaign did not respond to numerous requests for comment Saturday night on whether Trump had any evidence the explosion was a bomb or whether he was in contact with NYC officials.
On Sunday, the New York Joint Terrorism Task Force began investigating the bomb in New York as possible terrorist acts, as well as a similar blast in New Jersey. The Minnesota FBI also said they were investigating a knife attack there as a possible terrorist act.
Trump's Democratic opponent, Hillary Clinton, spoke to reporters in White Plains nearly two hours after the explosion and similarly called the incident a "bombing."
Clinton said she had been in touch with various New York City officials. She declined to answer a question about what effect, if any, the explosion would have on the 2016 race.
But asked about Trump's response, Clinton said: "I think it is important to know the facts about any incident like this. ... It is always wiser to wait until you have information before making conclusions, because we are just in the beginning stages of trying to determine what happened."
After the news came Sunday that the incidents were being investigated as terrorist acts, Clinton issued a statement condemning the attacks and touting her plan to combat ISIS, which laid claim to the Minnesota attack.
"I strongly condemn the apparent terrorist attacks in Minnesota, New Jersey, and New York. I pray for all of those who were wounded, and for their families," she said. "Law enforcement officials are working to identify who was behind the attacks in New York and New Jersey and we should give them the support they need to finish the job and bring those responsible to justice - we will not rest until that happens."
President Barack Obama, who spoke soon after Trump at the Congressional Black Caucus gala, made no mention of the incident. He was later briefed on the explosion, a White House official said.
A law enforcement source told CNN that the explosion occurred around 8:40 p.m. ET -- about 30 minutes before Trump took the stage here -- at 23rd Street and 6th Avenue in Manhattan. New York authorities said 29 people were injured in the explosion.
"We've got to get very tough," Trump said. "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."
Trump did not immediately exit his plane as he landed for his rally at an airplane hanger here. He was being briefed on the explosion in New York before he took the stage, a campaign aide told CNN.
Trump did not return to the reports of an explosion in New York during the rest of his speech.
But he also did not hold back his usual barrage of political attacks.
The Republican nominee gave a standard stump speech during which he repeatedly attacked Clinton over everything from her controversial use of a private email server during her time as secretary of state to what he deemed her coziness with big moneyed interests.
And he also suggested that former Defense Secretary Robert Gates, who slammed Trump in an editorial earlier Saturday, "probably has a problem we don't know about."
This story has been updated.