SYDNEY • Smoke from Australia's fierce bush fires settled over Sydney yesterday, setting off fire alarms, and halting ferry services as famous landmarks disappeared behind some of the worst haze seen in the New South Wales capital city.
A 60km firefront is devastating tinder-dry areas north-west of Australia's largest city, and sending hazardous smoke across the east and over the Pacific, even causing haze more than 2,000km away in New Zealand, satellite images show.
"This smoky period we've been experiencing for the past month or so is unprecedented, so these conditions are a risk to people's health," said Dr Richard Broome, the New South Wales government's director of environmental health.
He said that while many people would experience sore eyes, nose and throat irritations, those with pre-existing health conditions, and young children and the elderly were at particular risk.
Sydney's air quality index readings in some parts of the city yesterday were 11 times the threshold considered hazardous, government data showed.
The wildfires have blanketed Sydney - home to more than five million people and which is better known for its clear skies and blue harbour - in smoke and ash for more than two weeks.
That haze has turned the daytime sky orange, obscured visibility and prompted many commuters to wear breathing masks.
Bush fires are common in Australia's hot, dry summers, but the ferocity and early arrival of the fires last month in the southern hemisphere spring had been unprecedented. Experts say climate change has left bush land tinder-dry.
While there is no official evacuation order, many locals in areas that are under threat have decided to leave their homes, Hawkesbury Mayor Barry Calvert told Reuters.
"Many people have decided to leave, and I'm going to do the same," said Mr Calvert, who lives north-west of Sydney. "I've been through this before, about 20 years ago, when I stood outside my house looking at flames 15m high - I decided then that I would leave early if it happened again."
There are more than 100 fires ablaze in the eastern states of New South Wales, Victoria and Queensland. The fires have killed at least four people, destroyed more than 680 homes and razed more than one million ha of bush land.
Yesterday, Sydney's ferries, which started the day using foghorns as they cautiously moved through the thick smoke, were halted at lunch time as visibility fell even further.
The dense smoke even seeped into buildings, triggering alarms in offices and homes, and at train stations and on university campuses.
Australian wildfires have generated more hot spots in the past two days than any other country and the intensity of the blazes is greater than the next 10 worst-affected countries combined.
US space agency satellites have detected 5,837 hot spots in Australia over the past 48 hours.
Nasa operates Modis (moderate resolution imaging spectroradiometer) sensors aboard its orbiting satellites that circle the globe every two days and capture data about the Earth's surface and atmosphere.
In areas with wild fires, the instruments also measure the fire radiative power, an estimate of intensity of the blaze. The radiative power emitted from Australia is currently stronger than that of the fires raging across Central Africa or those in Brazil.