SYDNEY, Australia (AFP) — Thousands were 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 percent 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 organizer 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.

“People are experiencing it in their day-to-day lives.”

As well as a rise in people visiting hospitals with smoke-related health symptoms, the number of emergency calls for ambulances spiked 30 percent last week.

“For most people, smoke causes mild symptoms like sore eyes, nose and throat,” top health department official Richard Broome said.

“However, people with conditions like asthma, emphysema and angina are at greater risk because the smoke can trigger their symptoms.”

Smoke from bushfires is one of the biggest contributors to air pollution in Australia, releasing fine particles that can lodge deep within people’s lungs and cause “severe” health impacts over time, according to scientist Mick Meyer from government-funded scientific research agency CSIRO.

“The impact of smoke on people remote from the fires may, on occasion, substantially exceed the direct injury to people within the fire zone,” he wrote in The Conversation.

“But we currently lack the operational tools to understand the extent of these impacts or to manage them.”

Six people have been killed and more than 700 houses destroyed in bushfires this fire season.

Though the human toll has been far lower than the deadliest fire season in 2009 — when almost 200 people died — the scale of this year’s devastation has been widely described as unprecedented.