Yorkshire Ambulance Service issued the warning during in the early hours of this morning as it asked people who have already called for an ambulance not to call again to ask for a time of arrival.
“This could delay us speaking to a caller about a seriously ill or injured patient,” it said.
“Only call us back if the patient's condition worsens or they no longer need our help. Thank you for your support.”
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It did not give a reason for the high number of calls but this is the hottest weekend of the year and the first weekend of the summer holidays for many families.
The number of people being admitted to hospitals with Covid has also risen sharply over the last fortnight.
South Yorkshire Fire & Rescue said BT was reporting a ‘big increase’ in 999 calls generally, which it said was due in part to the hot weather.
“The very high volume of calls may result in a slight delay in some emergency calls being answered,” it said.
“BT has called on people to only call 999 if it's a genuine emergency to help keep call volumes low.”
Temperatures in Sheffield peaked at around 29C yesterday and today is expected to be just as hot, according to the Met Office.
Yorkshire Ambulance Service last night urged people to stay safe in the heat and avoid ending up in the back of an ambulance, saying: “Take care of yourself by drinking responsibly and staying hydrated.”