A spike in the number of people hospitalised across NSW with heat-related illnesses has prompted health experts to issue a warning ahead of more warm weather.
Sydney's west is forecast to reach the mid-30s while the mercury is tipped to hit 45C in other parts of the state on Friday.
NSW Health Environmental Health director Dr Richard Broome pleaded with people to limit their time outside during the hottest period of the day and keep an eye on those most vulnerable to the heat.
"During hot weather, it's important to stay in regular contact with elderly neighbours, friends and relatives, because helping them do basic chores to keep them out of the heat could make a life-saving difference," Dr Broome said in a statement.
"We've seen marked increases in ED presentations with heat-related illnesses over the last week or so."
He said initial signs of heat-related illness may include faintness, irritability, dark urine and later a rapid pulse, confusion and shallow breathing.
© AAP 2019