New York bombs both ‘pressure cookers’ as bomber remains at large ahead of UN summit hosted by Barack Obama

Investigators hunt for clues as New York prepares to host world leaders

(REUTERS)

Investigators continue to search for links between two bombs planted in the Chelsea area of Manhattan on Saturday night, one of which exploded injuring 29 people.

The bomber is still at large, and while officials are reported to have stopped a “vehicle of interest” and questioned its five occupants on Sunday, no arrests have been made.

Both the device that went off on West 23rd St, and the unexploded bomb found four blocks away on 27th Street, were described as being pressure cookers filled with shrapnel, the same method used in the Boston Marathon bombing in 2013.

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Governor Andrew Cuomo said the second device appeared “similar in design” to the first, though officials haven’t revealed any further details.

But separate US media reports, citing officials off the record, say both devices had flip phones and Christmas lights as makeshift detonators.

The 23rd St bomb contained residue of the explosive Tannerite, an FBI official said, a substance used for target practice that can be picked up in many sporting goods stores.

That differentiates the bombing from a pipe bomb blast in a New Jersey shore town earlier in the day, where a black material but no Tannerite was found.

Authorities said the Manhattan bombing and the blast 11 hours earlier at the site of a 5K race to benefit Marines and sailors in Seaside Park, New Jersey, didn't appear to be connected, though they weren't ruling anything out. The New Jersey race was cancelled and no one was injured.

But the three devices planted in the area came just days before world leaders descend on New York for a meeting of the UN general assembly.

Police said around 1,000 extra security personnel are being deployed to New York's transport hubs.

And New York Mayor Bill de Blasio said there would be a "bigger than ever" police presence in New York in the coming week.

“Was it a political motivation? A personal motivation? We do not know,” Mr De Blasio said.

"We know there was a bombing. We know it's a very serious incident. But we have a lot more work to do to be able to say what kind of motivation was behind this.

"All possible theories of what's happened here and how it connects will be looked at but we have no specific evidence at this point in time."

Late on Sunday, more suspicious devices were found near a train station in Elizabeth, New Jersey.

Elizabeth mayor Christian Bollwage said the devices were found in a bag in a rubbish bin by two men who reported seeing wires and a pipe coming out of the package.

There turned out to be five devices in the bag. One of the devices exploded as a bomb squad used a robot to try to disarm it. No injuries were reported.

There was no immediate word on whether the devices were similar to those in nearby Seaside Park or New York City