Image copyright EPA Image caption Many people are wearing face masks on the streets

A shroud of smoke from Australia's bushfires has caused chaos in Sydney, bringing dangerous air quality, setting off smoke alarms and ruining visibility in its typically sparkling harbour.

The haze on Tuesday was described by many people as the thickest to blanket the city amid this year's fire crisis.

It caused the cancellation of ferry and boat rides, while smoke permeating buildings forced evacuations citywide.

Locals described the situation as "apocalyptic" and "insane".

Image copyright Getty Images Image caption Sydney has been covered by thick smoke from bushfires outside of the city

Image copyright Getty Images Image caption The Sydney Harbour Bridge is almost entirely obscured by the smoke

Image copyright Getty Images Image caption The smoke from inland fires has reached all the way to the coast and Bondi Beach

Online, Sydney residents reported breathing problems and said they were "choking" on the smoke.

The city has endured air quality surpassing "hazardous" levels for weeks, as about 100 blazes continue to rage throughout New South Wales (NSW).

Video caption Sydney bushfire smog 'like being a heavy smoker'

The closest fires are about an hour's drive away from Greater Sydney, which has a population of five million people.

Tuesday was "the worst smoke day yet", according to locals on social media. In previous days, ash has fallen from the sky.

Image copyright Reuters Image caption On Friday, Sydney's Balmoral Beach was covered in ash from a bushfire 100km away

Video caption Imogen Brennan shared videos online of an Australian beach covered in ash

At its peak, air pollution in the city centre was 11 times worse than "hazardous" levels. It was even worse in suburbs and towns closer to the fires.

Several office buildings - including the headquarters of the NSW Rural Fire Service - were briefly evacuated after the smoke triggered indoor alarms.

Health officials advised people to stay indoors, while many who ventured outside donned face masks.

Hospital admissions have risen by at least 25% in the past weeks due to an influx of people with respiratory and breathing problems, officials said.

Image copyright EPA Image caption The smoke worsened throughout Tuesday as fires intensified

Image copyright Getty Images Image caption Not everyone has listened to warnings to avoid exercise outdoors

Image copyright Getty Images Image caption Trips on the city's harbour ferries were suspended due to the poor visibility

Daycare centres and schools were also keeping children inside during lunch and recess.

Last week, authorities said the stretch of air pollution was "the longest and most widespread" for the state on record.

"[We have] recorded some of the highest air pollution ever seen," the New South Wales government said.

Image copyright Getty Images Image caption Swimmers at a Sydney beachside pool on Tuesday morning

Image copyright Getty Images Image caption A man takes a picture of the city's disappearing skyline as he crosses the Sydney Harbour Bridge

Six people have died and more than 700 homes have been destroyed in bushfires that have ravaged Australia since September. More than two million hectares of land has been scorched in NSW alone, officials have said.

Public anger towards Australia's conservative government - and its efforts to address climate change -has grown as drought, water and bushfire emergencies have persisted.

Prime Minister Scott Morrison addressed media in Sydney on Tuesday but did not comment directly on the smoke's impact.

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