A bomb has exploded on a Manhattan subway underpass leaving four people injured in a suspected-Isil-inspired attack.

The suspected bomber is Akayed Ullah, a 27-year-old Bangladeshi national who first moved to the US in 2011.

He was pictured moments after the apparent attempted suicide attack crumpled in a heap with severe burns and lacerations to his torso and was later taken to hospital and placed under arrest.

CCTV footage shows the bomber walking down a tunnel armed with a five-inch metal pipe bomb and battery pack strapped to his body before a flash of smoke fills the walkway.

The bomb, described by authorities as a low-tech device, exploded inside the passageway to three metro line trains at an underpass to the Port Authority Bus Terminal near Times Square, the nation’s busiest bus station.

Who is the bomber?

Sources close to the investigation said Ullah first arrived in the country from Bangladesh on an F-4 visa, available to those with family in the US, around seven years ago.

The suspect, photographed lying face down, with tattered clothes and burns on his exposed torso, has been co-operating with police as he is treated at New York’s Bellevue Hospital.