A bomb squad was called to the Northeast Corridor train tracks in Elizabeth, New Jersey, after five explosive devices was found in a backpack.

But as a robot was working on the package, it exploded, according to a police officer at the scene – it was reportedly not a controlled blast, indicating it could have been triggered remotely.

Elizabeth Mayor, Chris Bollwage, said had the bomb not been discovered before it went off it "would have killed and hurt many".

There are not believed to be any casualties at this stage.

The suspicious item was found in the area of North Broad and Westfield Avenue by two men who were sifting through rubbish.

They noticed the device was hooked-up to a mobile phone and had sticking out of it and immediately alerted police.