Temperatures in Penrith are expected to hit 41 degrees today, ahead of a hot weekend with maximum temperatures of 38 and 39 predicted for Saturday and Sunday respectively in western Sydney.

A total fire ban is in place in the greater Sydney region until midnight, which includes the Blue Mountains, with a severe fire danger rating.

The NSW Department of Health has issued a poor air quality health alert for Sydney today.

The Ambulance Service of NSW offers the following advice for hot weather:

- Try to stay out of the sun, especially the eldery and the very young

- Drink plenty of water and take a bottle of water with you if outdoors for a long time

- ``Slip, slop, slap and wrap''

- Never leave children shut in the car. Heat in a closed car can lead to serious illness or death

- Feed breastfed infants more often to keep up their fluids

- Avoid outdoor exercise or strenuous physical activity, especially in the middle of the day

Be aware of possible symptoms of heat exhaustion, which may include nausea and vomiting, faintness, dizziness, loss of appetite, weakness and headache.

If any of these occur, the Ambulance Service advises laying the person down and applying cool, wet towels around the neck and under the arms and have them drink cool fluids.

Call triple zero (000) straight away and ask for an ambulance if the person does not respond to treatment or if they have severe symptoms such as confusion or if they collapse.