CANBERRA, Australia — Fire alarms have been sounding in high-rise buildings across downtown Sydney and Melbourne as dense smoke from distant wildfires confuses electronic sensors. Modern government office blocks in the Australian capital Canberra have been closed because the air inside is too dangerous for civil servants to breathe.

The sun has glowed an eerie red behind a brown-shrouded sky for weeks over Australian metropolitan areas that usually rank high on lists of the world’s most livable cities .

It’s an unprecedented dilemma for Australians accustomed to blue skies and sunny days that has raised fears for the long-term health consequences if prolonged exposure to choking smoke becomes the new summer norm. Similar concerns over smoke are emerging in other regions of the globe being impacted by more fires tied to climate change, including the Western U.S.

Canberra, as well as Australia’s two largest cities, Sydney and Melbourne, have at various times in recent weeks rated as the most polluted cities in the world, although some argue the industrial pollutants in places such as New Delhi are more dangerous than wood smoke.

Wood smoke contains some of the same toxic chemicals as urban air pollution, along with tiny particles of vapor and soot 30 times thinner than a human hair. These can infiltrate the bloodstream, potentially causing inflammation and blood vessel damage even in healthy people, research on urban air pollution has shown. Studies have linked heart attacks and cancer with long-term exposure to air pollution.

The fires have claimed at least 28 lives since September, destroyed more than 2,600 homes and razed more than 25.5 million acres, mostly in New South Wales state. The area burned is larger than the state of Indiana.

Rod McGuirk is an Associated Press writer.