A public health warning has been issued after a number of canisters were discarded across Sheffield that could contain gas that induces hallucinations, nerve damage and even death.
South Yorkshire Police said officers have discovered a number of nitrous oxide canisters discarded across the city recently and warned members of the public about the dangerous gases that could be contained inside.
They have not yet revealed how many have been found recently - but nearly 70 were found around Sheffield and Rotherham, while some were stolen from a hospital, in 2015.
The force said the substance, also known as laughing gas, is being inhaled by some people for its hallucinogenic effect. But they warned prolonged use can cause serious health problems and even be fatal.
A spokesperson for the Sheffield South East Local Policing Team said: "We have recently seen an increase in reports of small metallic canisters being discarded around the area.
"These are nitrous oxide canisters, the contents of which are being inhaled for their hallucinogenic effect.
"Heavy, prolonged use of this drug can cause anaemia, nerve damage, mobility problems and even death in some cases as the gas can seriously affect oxygen levels in the body."
The team shared a link to the Talk to Frank website, which offers advice for people suffering with drug problems.
The website warns: "Because nitrous oxide is a pressurised gas in the canister, there is a risk of harming yourself if you inhale nitrous oxide straight from the canister.
"This method can lead to sudden death due to a lack of oxygen and is one reason why nitrous oxide is sold to people in balloons."
Since the Psychoactive Substances Act came into effect in May last year, it is now illegal to supply or import nitrous oxide for human consumption.
In May this year, children were reportedly evacuated from an Islamic faith school in Darnall after gas canisters were discovered outside. It was not established at the time whether or not they contained nitrous oxide.
In June 2015, several gas canisters thought to have been containing the substance were stolen during the break-in at Thornbury Hospital on Fulwood Road.
Around the same time we reported how 50 canisters had been recovered in Green Lane, Ulley, with another 14 were found in Church Lane, Aston. Further canisters were also discovered in Barbers Field, Woodseats.