Animal charities have issued a stark warning to cat owners living in properties one-storey high or above, urging vigilance against potentially fatal falls during hot weather.

Cases of “high-rise syndrome”, where felines sustain injuries from falling from elevated positions, typically spike in summer as indoor cats are enticed outdoors by warmer temperatures, birds, and movement.

Both Cats Protection and Blue Cross have cautioned pet owners against leaving windows and balconies open and unattended.

Blue Cross animal hospitals in London and Grimsby have already treated 33 cats this year for injuries suffered in such falls.

The warning comes as the UK braces for heatwave conditions to return next week, with a high of 36C expected in parts of East Anglia and south-east England by Thursday.

With people likely to open windows and doors to balconies, the charities have warned that younger and more curious indoor cats, especially unneutered males, may be particularly at risk of falling from height as they are more tempted to roam outside.

Alliah Seed’s three-month-old kitten Sapphire was “very lucky” to only suffer a fractured toe after falling from the window ledge of a fifth-storey flat.

Ms Seed took Sapphire to the Blue Cross animal hospital in Victoria, central London, fearing the worst after her pet collapsed with dried blood around her nostrils.

“Sapphire has been used to resting on the windowsill and getting fresh air with no problems until now,” Ms Seed said.

“I was totally shocked when she fell, she must have been spooked or something.”

Izzy Hocking, a veterinary engagement manager at Cats Protection, said that cats can twist in mid-air – but they will not always land safely.

“You might think that cats naturally understand the dangers of heights, but this is not always true,” she said.

“Cats living in flats, particularly those who have never experienced the outdoors, do not recognise the risks posed by open windows, doors or balconies.”

She added: “Depending on the height it falls from, a cat could suffer severe injuries such as broken limbs, jaw fractures and internal trauma including brain damage.

“In some cases, falls can prove fatal or result in euthanasia due to the severity of injuries.”

Blue Cross and Cats Protection advised owners of indoor cats to fit secure netting or screens over windows, doors and balconies to reduce the risk of falls.

Open windows should not be left unattended, especially overnight, and cats should be neutered to reduce roaming behaviours.

Indoor enrichment such as toys or cat trees, walkways and shelves can also help preventing an indoor cat from wanting to go outside by keeping them entertained and active.

“I’m soon moving to a ground floor flat but I will still put up mesh to prevent her from falling or jumping outside again,” Ms Seed said.

“Cat owners living in blocks of flats really should do the same to prevent terrible and potentially tragic accidents.”

Roisin Bolger, veterinary standards lead at Blue Cross, said: “Even from a relatively low storey, cats may break several bones or land somewhere dangerous like a spiked railing or on to dangerous objects below.

“Injuries will often need extensive surgery and a lengthy stay in hospital.

“Cat owners really must take measures to prevent their pet from falling from a window or balcony to prevent suffering or death.”