Forecasters have cancelled severe weather warnings for the Sydney and surrounding regions after more than 17,000 homes and businesses in the Harbour City were left without power.

Key points: The severe weather warning for Sydney has been cancelled, parts of the mid north coast may still be battered

The severe weather warning for Sydney has been cancelled, parts of the mid north coast may still be battered Air quality has deteriorated in Sydney as a dust storm sweeps across to the coast

Air quality has deteriorated in Sydney as a dust storm sweeps across to the coast Ausgrid says most of the 17,500 properties without power are on the north shore

Health authorities had also warned a dust storm sweeping across the state was closing in on Sydney, affecting air quality levels.

Severe storms were detected near Richmond and Windsor in the early afternoon but by 5:00pm the Bureau of Meteorology (BOM) cancelled a warning that covered the greater Sydney region.

The threat moved north, with residents of the mid north coast, Hunter, north west slopes and northern tablelands warned of potentially damaging winds.

Ausgrid said it was working to restore power to 17,500 properties across Sydney's north and lower north shore.

NSW Health earlier told people with respiratory and cardiovascular conditions to steer clear of strenuous outdoor activities due to the approaching dust, and said air quality was likely to worsen during the day.

Gundagai was badly impacted by the dust storm. ( Supplied: Facebook )

Sydney's air quality was rated as "poor" today.

"Dust may aggravate existing heart and lung conditions and cause symptoms like irritated eyes and a cough," said Director of Environmental Health Dr Richard Broome.

"People with conditions including asthma, chronic bronchitis, emphysema and heart disease should monitor their symptoms throughout the day."

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He said symptoms can occur for several days after dust is inhaled and if they don't settle, people are advised to seek medical advice.

Dust, rain wreak havoc with motorists

The Riverina has been the worst hit by the dust, with air quality reaching hazardous levels over the past 24 hours near Wagga Wagga and Albury, while areas around Bathurst and Orange suffered very poor air quality conditions.

Residents of Bomen and Coota captured spectacular images of the enormous dust cloud encapsulating their suburbs.

As rain scattered across the Riverina and mixed with the dust, drivers were forced to pull over as their windscreens became covered in mud.

Photographer Straun Timms captured the wall of sand near Wagga yesterday as it rapidly approached the town of Junee.

"It was epic," Mr Timms said.

"It was a very fast-moving storm that brought a lot of thunder and lightning — a great wall of purple sand.

"Within two minutes of taking the photo, it was already on us and we got out of there."

The south west slopes region, including Wagga Wagga, recorded hazardous particle levels on Wednesday even after conditions were calmer.

When particles reach that level, the state's Environment Department advises everyone to avoid outdoor exertion and stay inside as much as possible.

The conditions can be especially problematic for anyone with heart or lung diseases.

Forecasters said a cold front would extend across the southern inland and western districts on Wednesday afternoon.

This was expected to bring cooler conditions, along with some showers and thunderstorms to much of the state.