Vic heat hits Australian Open spectators

Almost 1000 people have been treated for heat-related illness at the Australian Open as the Victorian heatwave continues.

Emergency Services Minister Kim Wells said St John's Ambulance staff have treated 970 tennis fans for heat exhaustion during the tournament.

Australian Open organisers invoked the extreme-heat policy for the first time on Thursday afternoon as temperatures topped 43C.

Victoria's ambulance service is also recording a spike in heat-related cases with paramedics treating 243 people between Monday and midday on Thursday, an eight-fold increase.

Ambulance Victoria operations manager Paul Holman said Victorians need to think about their situation before calling an ambulance, with paramedics receiving one phone call about a sore throat.

"If you are suffering chest pain or any other serious medical condition, then certainly call triple-zero.

"However if it is something less urgent then just think about whether a doctor, Nurse On Call, a relative or some other service is more appropriate."

The state has also had a jump in cardiac arrests, with 26 cases on Wednesday and another 28 before 4pm (AEDT) on Thursday.