Ambulance chiefs have urged the public not to ring 999 if they felt "hot and sweaty" after a 25 per cent increase in calls.
South Yorkshire Ambulance Service said they had been inundated with emergency calls from people across the region as the temperatures soared over the last few days.
On Sunday, the service saw an increase of 25 per cent in 999 calls over the day - similar to the volume of calls on a busy New Year's Eve.
Liz Howarth, the service's director of corporate development said: "Many people are calling with complaints that they are 'hot and sweaty', which is to be expected in this weather, and we would ask people to consider other forms of help and advice before dialling 999.
"Whilst we do not want to deter people who have a real emergency, people need to consider whether dialling 999 for an ambulance is appropriate for any care they need."
She said NHS Direct was available 24 hours for telephone advice and support and is able to signpost people to the most appropriate service if they have a health need.
Forecaster Rachel Vince said Sunday was the hottest day of the year so far, with temperatures reaching 33C in London and the low 30s in Yorkshire, before they cooled slightly at the start of the week.
She said: "As of yesterday, the temperatures picked up again, along with the humidity, and it's probably a combination of these that's making people feel uncomfortable."
Yesterday, temperatures reached 28C in Rotherham, South Yorkshire, but forecasters warned that the summer heatwave was set to give way to torrential rain and flooding.