Updated, 15.28

INVESTIGATORS INTO SATURDAY’S bus crash in New York City, in which 15 people were killed, are trying to establish whether driver fatigue may have been to blame for the accident.

The 15 passengers lost their lives when their bus veered off the road, before flipping on its side and having its roof sliced off by a massive signpost in the Bronx in the early hours of Saturday morning.

AM New York reports, however, that while the National Transportation Safety Board is examining the bus for possible mechanical problems, it is also probing whether the driver had been too tired to take the wheel at the time of the accident.

Though driver Ophadell Williams claimed the bus had been struck by a tractor-trailer – causing it to veer off the road – police sources told the New York Post they could not find any evidence on the bus of a collision.

A truck driver told police the bus was moving erratically, though Williams passed breathalyser tests taken at the scene.

The bus, which was carrying tourists to the Chinatown area of Manhattan when the accident occurred at around 5:30am local time, had been travelling tourists from a casino in Connecticut.

Police are also still trying to identify one survivor who was critically injured in Saturday’s crash; the man, 50, has been unconscious since the accident and remains on life support machines.

He has not been able to speak, due to a breathing tube being placed down his throat, but officers fear that they will not be able to confirm his identify unless he wakes up and speaks to them.