NSW Health has warned people to stay cool as high heat and ozone pollution hits Sydney and other parts of the state in the lead up to the new year.
Hot and sunny conditions are forecast for Sydney on Boxing Day and beyond, with the mercury tipped to hover above 30C in the dying days of 2018.
NSW Health executive director Jeremy McAnulty warned people to be prepared for the first real heat of summer.
"It's important to keep up water intake, stay cool and avoid strenuous physical activity in the heat of the day because heat places a lot of strain on the body and cause dehydration, heat exhaustion and heat stroke," he said in a statement on Wednesday.
Sydney is expected to reach 28 degrees on Boxing Day before the temperatures climb to the low 30s ahead of New Years Eve, according to the Bureau of Meteorology.
In Western Sydney and inland parts of NSW the mercury will top 40C.
While clear, sunny conditions have been forecast, an air quality warning has been issued for Boxing Day, with ozone levels forecast to exceed national air standard qualities.
Dr McAnulty said ozone could irritate the lungs and people with asthma needed to follow their action plan and take their relieving medication as necessary.
He asked people to be aware of the vulnerable such as infants, children and the elderly, people with chronic health conditions and those who lived alone.
The last day of the year is forecast to be partly cloudy, with a slight chance of a shower.
