A US man decapitated his mother and dragged her headless body into the street – but neighbours thought the horrific scene was a Halloween prank.

Derek Ward, 35, killed 66-year-old Patricia in their apartment in the Long Island town of Farmingdale on Tuesday night, the Daily News reported, citing police.

He then threw her body and severed head out onto the street at around 8pm, before allegedly killing himself by jumping in front of a train.

Nassau County Police Detective Lieutenant John Azzata said in a press conference: “There were multiple signs of trauma, multiple stab wounds, broken ribs.

“The weapon used was believed to be a knife. That knife was recovered.”

Witnesses to the aftermath of the murder said they did not comprehend the horror of what they had seen.

One resident told CBS: “You figure, OK, someone is playing a Halloween prank, but for it to turn out to be a reality - wow.”

Mr Ward reportedly had a history of mental health problems stretching back over the past decade and had been arrested in the past for criminal mischief, as well as weapons and drug possession.

However, there was no record of previous domestic incidents involving Mr Ward and his mother.

Ms Ward was a language arts professor at Farmingdale State College. Patrick Calabria, vice president of institutional advancement and enrolment management at the university said: “We are all in shock.