A Sydney mother will face court after she allegedly left her four children locked in a car in searing heat as she went shopping.

A witness called police after noticing the four children, aged six, seven, eight and nine, in the vehicle in a Bankstown car park on Wednesday afternoon at 3pm.

Police say the children were distressed but uninjured, while their 44-year-old mother will face court next month.

Temperatures in parts of western Sydney topped 40C on Wednesday.

Police have reminded parents that on a typical summer day, the temperature inside a car, even with the windows rolled down a little, can quickly rise above 50C.

Even on a relatively mild day, the temperature inside a car can get above 40C and at those temperatures, children are at great risk for heat stroke, which can lead to a high fever, dehydration, seizures, stroke and death.

Wednesday was the fifth day this summer that temperatures were over 35 degrees, the most since the summer of 1991-1992.

The woman is due to appear in Bankstown Local Court on February 22.

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