Sydney turns orange as dust storm chokes city

A dust storm rolled through Sydney overnight, enveloping the city in an orange cloud before a southerly buster brought a welcome cool change and relief for firefighters.

Plumes of orange dust blew across the city, shrouding cars in orange dirt and causing problems for paramedics who received an increase in calls to emergency services.

The Bureau of Meteorology's Rebecca Kamitakahara said while Sydney would enjoy cooler weather on Friday thans to the southerly change, Sydney still had to swelter through temperatures of 29C until 2am.

Dust was thick in the air at Sydney Olympic Park overnight. Picture: Damian Hofman

"The southerly slowly moved across the basin between 2 and 4am and up until that point we still had a warm air mass sitting across Sydney," she said.

Sydney can on Friday expect a top of 28C and the chance of showers and thunderstorms.

These conditions will linger across most of the state next week, with temperatures in the high-20s and 30s set to continue until Thursday.

Cars parked at Campbelltown Station were covered as plumes of dust blew across western Sydney. Picture: David Campbell

The favourable conditions are good news for fire crews, with the bushfire danger dropping overnight after a difficult day which saw three US tanker pilots killed in a devastating crash.

While temperatures have eased from yesterday's tops of 43C, the southerly overnight has dragged in a thick smoke haze.

A poor air quality alert has been issued as smoke from more than 70 fires burning across NSW blankets the state.

The fire in West Queenbeyan, 10km west of Canberra, quickly went to emergency levels yesterday as it threatened homes and the airport. Picture: AAP

Sydney woke to the acrid stench of smoke as the level of PM2.5 - particles in smoke which aggravate the lungs and heart - hit hazardous levels.

Air quality across Sydney's east, northwest and southwest is 10 times what's considered safe.

In the Illawarra, Hunter North-West Slopes and Central Tablelands air quality is also poor.

Health authorities are urging people - particularly those at higher risk - to stay indoors, reduce outdoor exercise and wear well-fitted P2 face masks.

Air quality is once again hazardous across Sydney as a southerly buster drags in smoke from the bushfires. Picture: Jenny Evans/Getty Images

Immediate exposure to bushfire smoke can aggravate lung or heart conditions and over several weeks or months can increase the risk of lung disease. For some pregnant women, a few weeks of exposure can reduce birth weight of their babies.

The smoke will linger for the rest of the day before easing over the weekend with north-easterly winds, Ms Kamitakahara said.