The unprecedented conditions led to visibility dropping to less than a kilometre in parts of Sydney such as Oakdale in the south-west, which is close to bushfires. Visibility is considered poor when it drops to less than 9 kilometres. Ultra-fine particle pollution, which health authorities warn can exacerbate asthma and other pulmonary or cardiac conditions, were also at "hazardous" levels across the entire Sydney basin for extended periods. In some parts, air quality readings were more than five times hazardous levels. AMP Capital chief economist Shane Oliver said the impact of the bushfires and smoke on the country's economy would start to sharpen the longer the conditions continued. "It seems to be getting worse, and not better. There is no doubt it is going to have an economic impact," he said. The blanket of smoke makes conditions in Sydney's CBD unpleasant for people during lunch time. Credit:Peter Rae Paramedics experienced an "elevated level of demand" due to the smoke, including from asthmatics who did not have their medication with them. NSW Ambulance received more than 150 instances of respiratory illnesses a day in recent weeks.

Sydney schools cancelled outdoor excursions and scheduled sports games, and most kept students indoors during lunch. The Department of Education said schools would consider alternative arrangements for staff and students in "extreme situations" where an entire school was heavily affected by smoke. The smoke triggered fire alarms at buildings and train stations across the city. Fire Brigade Employees' Union state secretary Leighton Drury said firefighters attended four times the number of false alarms they would be called to on any other day, because of the latent smoke. Firefighters attend scores of call outs at buildings across the city after the smoke triggered fire alarms. Credit:Peter Rae

"We normally do about 120 a day, but from midnight to 1pm we've had 250 and there are still another 12 hours," he said. "We need more resources to cover this stuff. We are still having to cover all the standard things like industrial accidents and rescues as well as the bushfires." Loading The thick smoke forced the suspension of ferry services, while poor visibility at Sydney Airport caused flight delays of up to 30 minutes for several hours. A fire alarm was also triggered by smoke seeping into a terminal building. Alarms were also triggered at five train stations including Chatswood and Leppington. The smoke led to thousands of construction workers, electricians and apprentices abandoning work sites. The Electrical Trades Union said up to 1000 electricians and apprentices had left building sites including at Central Station and Westmead Hospital.

"Most sites have left and gone home after having safety checks. I haven't experienced this level of smoke before," Electrical Trades Union national secretary Allen Hicks said. "Bushfire smoke is especially hazardous for those doing strenuous outdoor work." Many people donned face masks on Tuesday. Credit:Peter Rae Unions NSW assistant secretary Thomas Costa said nobody, apart from emergency service workers who had accepted the risk, should be forced to work outside. "The current level of toxicity in the air is 10 times the safe working limit," he said. The Sydney University branch of the National Tertiary Education Union advised members to stop work or make alternative arrangements if they were concerned about air quality in their workplace. Health authorities said Sydney had suffered "some of the worst air quality we've seen" and urged the public to take the conditions seriously.

"When conditions are like this people should avoid outdoor activity as best as they can. Young children are also at more risk because they have developing lungs," NSW Health's director of environmental health Richard Broome said. Loading Replay Replay video Play video Play video "The smoke we've been experiencing for the last month or so is certainly unprecedented." NSW chief health officer Kerry Chant urged people with underlying respiratory conditions such as asthma and heart disease to take particular care. The City of Sydney took measures to help homeless people affected, including providing temporary accommodation for those who suffered from existing respiratory conditions.