Five suspicious devices have been found near a train station in New Jersey, with one exploding during attempts to disarm it.
The moment the device disappeared in a fireball, as FBI bomb squad robots moved in, was caught on film.
The blast came as five men were detained and questioned over a bomb attack in New York on Saturday night, which left 29 injured.
It has been reported the device that detonated in Manhattan, and another device found nearby that failed to go off, were both shrapnel-filled pressure cookers, similar to those used in the attack on the Boston Marathon in 2013.
The latest device was found in the early hours of Monday in the city of Elizabeth, less than 15 miles southwest of Manhattan, after two men found a backpack containing the suspect devices in a bin.
The city's mayor, Christian Bollwage, told Sky News the pair had alerted authorities after they "saw wires and a pipe".
Up to five devices were found in the bag and when the robot cut a wire on one of them to try and disable it, it exploded.
Mr Bollange said: "I can imagine that if all five of them went off at the same time, that the loss of life could have been enormous if there was an event going on."
The discovery came after a small pipe bomb exploded in the New Jersey town of Seaside Park on Saturday morning, shortly before a charity run for US marines and sailors. No one was injured.
Later that day a knife-wielding man injured eight people at a shopping mall in Minnesota, before he was shot and killed by an off-duty police officer.
Islamic State has claimed he was a "soldier" of the terror group.
As part of the inquiry into Saturday's bombing in Manhattan, the FBI pulled over a car described by officials as "a vehicle of interest in the investigation" in Brooklyn on Sunday night.
five occupants are being questioned at an FBI building in Lower Manhattan.
However, no-one has been charged and the investigation is continuing.
Forensics experts are continuing to comb through evidence from the Manhattan bombing, which was described by witnesses as a deafening blast that shattered windows and hit bystanders with shrapnel.
All of those who were injured by the explosion had been released from hospital by Sunday afternoon.
Meanwhile, CNN has reported surveillance videos showed the same man close to the site of the first explosion and the location where the unexploded device was found.
The discovery of the latest device comes as nearly a thousand extra police are deployed on New York's streets as world leaders arrive in the city for a UN summit on the refugee crisis.
Latest developments:
- Device explodes in Elizabeth, New Jersey
- Surveillance video may show the same man at both New York locations where devices were found
- Governor orders 1,000 state troopers and National Guard soldiers to New York City
- Authorities investigating 911 call claiming responsibility
- Officials attempting to identify suspects from surveillance video
- Both NYC "bomb" and explosive device in New Jersey used flip-phones
