Thousands are expected to rally in Sydney on Wednesday to demand urgent climate action from Australia’s government, as bushfire smoke choking the city caused health problems to spike.

Smoke alarms rang out across Australia’s biggest city Tuesday with thick haze from bushfires burning along the country’s east coast forced buildings to be evacuated, school children to be kept indoors, and ferries to be cancelled.

Sydney has endured weeks bathed in toxic smoke as hundreds of blazes have raged across the countryside, with hospitals recording a 25 per cent increase in the number of people visiting emergency departments last week.

The devastating fires have focused attention on climate change, with scientists saying the blazes have come earlier and with more intensity than usual due to global warming and a prolonged drought.

At least 5,000 people were expected at Wednesday’s protest, according to organiser Chloe Rafferty, who said the bushfires and smoke haze had created anger at the conservative government’s inaction on curbing emissions.

“I think the wider public can see that we are not expecting the climate crisis in the future but we are facing the climate crisis now,” she told AFP.

Six people have been killed, hundreds of homes destroyed and more than 1.5 million hectares (3.7 million acres) scorched across Australia since early October.

Dozens of fires also burn in the neighbouring state of Queensland and authorities had ordered an evacuation in towns such as Noosa North Shore and Woodgate.

The fires have been fuelled by tinder-dry conditions after three years of drought that experts say has been exacerbated by climate change, a factor that has sparked a sharp political debate in recent days.

About 70 fires were burning in the state, with Pechey residents told the safest option was to leave the area as conditions are currently too dangerous.

More than 1,800 firefighters were battling those blazes, 66 of which were uncontained.