Passengers on a New York City subway were left horrified when their car filled with fumes after a fellow passenger lit up and proceeded to smoke what appeared to be hard drugs.

The unidentified man, who was travelling on the Lexington Avenue Line - the 6 train - in Manhattan, was described by fellow commuters as smoking a substance which was 'definitely not legal.'

The incident took place at around noon on Tuesday and passengers looked on in shock as the smell of smoke spread across the car as it traveled underneath New York's affluent Upper East Side.

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Horror: Passengers on a New York City subway were left horrified when their car filled with fumes after a fellow passenger lit up and proceeded to smoke what appeared to be hard drugs

Detritus: The 'drug-smoking' man was surrounded by debris as he sat on the lunchtime local train going from Pelham Bay Park in the Bronx to Brooklyn Bridge-City Hall station. Mayor de Blasio has presided over rising transit crime in the last year.

A commuter said to Daily Mail Online: 'It made me feel instantly nauseous. I know the smell of pot and it definitely wasn't that. It was highly toxic and everyone in the car smelt it as soon as it was lit.

'We were convinced it was either some form of meth or crack cocaine. People were covering their mouths with their hands and clothing.'

One passenger on the 12.30pm train heading downtown to its final stop of Brooklyn Bridge City Hall, took pictures of the man, who was oblivious as he continued to both roll and smoke the substance.

As the car pulled into the 68th street station, passengers including a mother with a young child, senior citizens and lunch time commuters, quickly escaped to the second last car of the train.

The smoker stayed in the last car and then disembarked at the 59th Street station.

Anger: A commuter said to Daily Mail Online: 'It made me feel instantly nauseous. I know the smell of pot and it definitely wasn't that. It was highly toxic and everyone in the car smelt it as soon as it was lit. We were convinced it was either some form of meth or crack cocaine'

Destination: The smoker stayed in the last car and then disembarked at the 59th Street station

A passenger said: 'On a daily basis we're confronted with drunks, homeless people and panhandlers when all you want to do is get on with your business.

'The subway has become a complete zoo.'

There is increasing concern in the city that the 'broken windows' policing introduced in the 1990s is being diluted - especially after transit crime was revealed to have increased six per cent in a year earlier this month.

It ended the years, which began in the 1960s and got worse in the 1970s and 1980s, in which the subway was vandalized and dangerous, and passengers were regularly exposed to crime.

The policy was introduced first by current NYPD commissioner Bill Bratton when he was in charge of policing the subway from 1990 onwards, then taken up across the city by get-tough mayor Rudolph Giuliani.

It was continued under his successor Mike Bloomberg, but the two-year tenure of the latest mayor, Bill de Blasio, has been accompanied by concern that arrests for minor offenses - the backbone of 'broken windows' policing - are down.

In charge: NYPD Commissioner Bill Bratton (center) and Mayor Bill de Blasio (right) have presided over an increase in serious crime on the subway - and a fall in arrests for low-level offenses in the last year

De Blasio has also struggled to deal with a rising tide of street homelessness, with Bratton this week rebuking him for his failure to acknowledge the issue, saying it was a 'mistake' not to recognize it sooner than this month.

The mayor, elected on a platform of police reform and the idea that there are 'two cities' - of rich and poor - has faced criticism that falling official overall crime rates are actually masking a return of the disorder which characterized the city in the 1970s and 1980s.

Earlier this month, CBS New York reported that at the same time as robberies, felony assaults and grand larcenies all being up, arrests are down.

Under broken windows policing, the belief is that stopping low-level offenses by arresting everyone carrying them out leads to more serious crime being stamped out.

Another passenger said to Daily Mail Online: 'Only in New York would this happen. Broad day light, kids and old folk in the train and this bum lights up and smokes what appears to be hard drugs without a care in the world.'

'The smell was absolutely disgusting and I couldn't work out if it was crack cocaine or meth. I just wanted to escape that train car.'