A new warning over the dangers of inhaling "laughing gas" has been issued after dozens of used cannisters were found in the historic heart of Leicester.
The discarded silver cannisters were discovered in Castle View, next to the Newarke Houses Museum this week.
Most had been removed today, although one or two were still dotted around the area.
The gas, which can be bought legally in small canisters and has practical industrial uses, produces a euphoria but floods users' lungs and can cause unconsciousness or death due to a lack of oxygen.
Police have stepped up patrols in parks and streets across the city and county where they have evidence of people using nitrous oxide.
Warning signs have been put up in areas – typically parks and open spaces – where officers believe people are gathering to use it.
The campaign is part of the ongoing Operation Nitrox – which was launched by the force last year to highlight the risks of so-called legal highs.
Police said the Castle View area was not a known hotspot for its use.
Resident Gordon Palmer, 63, said: "I noticed these little cannisters the other day, there were dozens of them.
"I didn't know what they were at first, so I looked it up on the internet and saw a lot of young people are doing this dangerous thing.
"It's such a shame that people would resort to doing this in the most historic part of the city."
A woman who works in the area said: "It's such a lovely and important area of the city and it shouldn't be littered like this.
"Stacey McSharry, Leicestershire Police's substance misuse officer, said police were reporting a growing number of discarded canisters.
She told the Leicester Mercury earlier this year: "On the back of Operation Nitrox, we had a massive increase in intelligence from officers and other organisations about these substances.
"That is positive because it is giving us the information we need to take action."
Operation Nitrox was launched to highlight the risks of so-called legal highs – the chemical substances which were banned under legislation which was introduced last week.
For more details, visit:www.leics.police.uk/nitrousoxide
