Horrifying moment passenger is slashed in the face on New York LIRR train in front of terrified passengers before a brave man dives in and beats the attacker with his SHOE

A train passenger was slashed in the face over a petty dispute in a brazen daylight attack in front of shocked commuters.

Horrifying video shows the attacker on top of his victim laying into him as he tried to defend himself on the Long Island Rail Road in Queens on Monday.

A third passenger ran into the fray, diving on top of the attacker and punching him until he was thrown off across the aisle.

Then he tried to grab the 32-year-old man, who was armed with a box cutter, and pull him off the victim, but wasn't able to get a good grip.

A third passenger ran into the fray, diving on top of the attacker and punching him until he was thrown off across the aisle

At some point during the melee, the third man's shoe fell off - so he picked it up and repeatedly belted the attacker with it.

Eventually he was able to grapple the man and pull him off the victim, holding him at arms length as he tried to talk some sense into him.

The 27-year-old victim is not seen in the video until the man has been hauled off him, and waves his arms around above the seats.

Police said the older man slashed the victim in the face with the box cutter, and was arrested at the scene.

A woman who filmed the attack about 3.45pm said the petty dispute began a little earlier at Jamaica Center on the way to Far Rockway.

'The suspect was blocking the door when entering the train and the man whose face was slashed got into with him over him blocking the entrance,' she said.

The third man jumped on top of the attacker, punching him in an effort to break up the fight until he was able to grapple the man and pull him off the victim, holding him at arms length as he tried to talk some sense into him

The younger man sat down, but the attacker later walked over and began a verbal argument that escalated into violence.

'There was one boy who witnessed everything on that car and he was crying and scared to get back on the train when the new one pulled into the station,' the woman said.

'The conductor was comforting him and his mother. It was saddening.'

The train was stopped for 50 minutes while police investigated, and the victim was taken to Jamaica Hospital.

'Weapons have no place on trains, and we are grateful for the rapid response of NYPD officers who kept passengers safe and arrested the perpetrator,' the MTA said.