A bomb that exploded in New York City was an act of terrorism, New York Governor Andrew Cuomo says, but no link to international groups has been found, The Associated Press reported.

Cuomo said the bomb caused significant damage and "we were lucky there were no fatalities."

Saturday night's blast in Manhattan injured 29 people. Some 1,000 extra security personnel were deployed to transportation hubs.

"Whoever placed these bombs - we will find them and they will be brought to justice," Cuomo said.

Sources told CNN that videos show the same man near the sites of both incidents.

Police have been scouring the area for clues. The NYPD Bomb Squad and Joint Terrorism Task Force were called to the scene.

The blast happened at about 8:30 pm on West 23rd Street between Sixth and Seventh avenues.

A second device was found four blocks from the site of the explosion in the Chelsea district and safely removed by a robot.

Only one of the 29 injuries from the blast was serious, said New York Police Department Commissioner James O'Neill, who spoke in a televised news conference around 11:15 pm Saturday.

New York Mayor Bill de Blasio said there was no specific connection to an incident in New Jersey in which a pipe bomb exploded earlier Saturday at a charity run. No one was injured.

"We do have video," O'Neill said, "and we see the explosion, and we're going to use that to help us with the investigation."

A law enforcement official told The Associated Press that the second device, found in a plastic bag, appeared to be a pressure cooker attached to wiring and a cellphone.

Pressure cooker bombs have been used in a number of attacks, including the 2010 Times Square car bombing attempt, when it failed to explode, and the 2013 Boston Marathon bombings.

De Blasio said he wanted to assure all New Yorkers that the NYPD and all other agencies are "at full alert, and that our anti-terror capacity in particular is at full alert".

A taxi driver who gave his name as Saqib told China Daily that he saw people running after the blast happened. "It was terrible," said the 44-year-old, who has lived in New York for 29 years. "Many people are waiting for a cab. Restaurants are empty."

A Chinese student who gave his name as Zhou said the blast has left "a psychological shadow" in him. "From now on, I will be very careful with trash cans," said the freshman who hails from Jiangsu province.

New York City police said they were going to blow up the second device in a controlled detonation at a police facility in the Bronx on Sunday evening.

Police have not said what, if any, forensic evidence they've collected from that device.

Hillary Clinton condemned what she called "apparent terrorist attacks" in New York, New Jersey and Minnesota.

Officials in New York said Sunday they were still trying to determine who was behind the explosion and what the motivation was. New Jersey law enforcement would not say if a pipe bomb that exploded at a seaside community was terror-related.

Officials said an attack at a Minnesota mall in which a man stabbed nine people was being investigated as a possible act of terrorism; an Islamic State-run news agency called the attacker a "soldier of the Islamic State".

AP and William Hennelly contributed to this story.

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