‘Life-threatening’ Sydney heatwave

Sydney has been warned of a potentially deadly heatwave tomorrow and Saturday, with doctors urging everyone, especially older people, to have an emergency plan for keeping cool.

But high temperatures aren’t the only threat. Police also fear an outbreak of alcohol-fuelled violence.

One hundred people died during Sydney's 2011 heatwave, and doctors say this Summer could be worse.

“What we tend to see are increases in the rate of heart attack, increases in the rate of asthma, more falls than usual,” Dr Richard Broome said.

The Health Department is urging people to drink lots of cold water, to use air conditioning, and take it easy. Also, keep an eye on children, the elderly, and pets.

Police are prepared for alcohol-related violence, with 130 extra officers in the city, and at the V8 racing.

"Understand that in these heat conditions you may, if you're not careful, be drinking more than you usually would," Assistant Police Commissioner Alan Clarke said.

Police also warn it's a criminal offence to leave kids, or pets, in the car.

The heatwave has already hit three states, South Australia is under a total fire ban, and 44 degree heat is forecast for parts of Victoria.

Penrith will hit 40 tomorrow, and 41 for the start of Summer.

Despite the heat, firefighters say humid conditions will help reduce the bushfire risk.