SYDNEY (XINHUA) - Brown haze engulfed Sydney on Thursday (Nov 22), and the authorities are advising residents to take precautions.

The New South Wales Department of Health has issued a warning stating that tiny dust particles can penetrate deep into people's lungs, and suggesting that those with respiratory conditions stay indoors for the duration of the event, which is expected to dissipate by Friday.

"Some of the dust particles in the dust storm will be very small and can get deep into your lungs, and that's why we're concerned about people's health," director of environmental health Richard Broome said.

"Dust may aggravate existing heart and lung conditions and cause symptoms like eye irritation and cough. If possible, stay in air-conditioned places where filtration systems can help to reduce dust particles in the air," the director said.

The dust comes from further inland areas of the state, where winds from a low pressure system have whipped up the dry, drought-ridden soil and carried it all the way to the coast.

In parts of the state further west, visibility was severely limited as dense clouds descended on communities, although residents in many of those areas are more accustomed to dust events.

Conditions in Sydney are expected to peak on Thursday afternoon before clearing.