A public health warning was issued Thursday as a massive dust storm engulfed Sydney and other parts of the eastern Australian state of New South Wales.

Many locals took to social media to post photos of the city's skyline, which was blanketed by an orange haze largely due to strong winds from a low pressure system carrying thick dust across the drought-stricken state.

The storm, which stretches 500 kilometres, has reduced visibility to just metres in some areas, the Bureau of Meteorology (BOM) said.

State health authority NSW Health issued a warning, saying the dust would likely reduce air quality and that children, older people and those with respiratory conditions should take extra care.

"It’s a serious situation from an air quality point of view," Richard Broome, the department's environmental health director, told Australian broadcaster ABC.

He said people should stay indoors as much as possible as dust particles could aggravate asthma, lung and heart conditions and could cause eye irritations and coughing.

"It's going to be very windy and unpleasant later today, but the system is going to be moving east into the ocean and clearing overnight," BOM forecaster Anita Pyne told local media.

Dust storms are common in parts of rural Australia, however a storm of this size in a coastal city is considered unusual.