In its latest update, the State Department revised the advisory to Level One meaning “exercise normal precautions”, however it maintained a Level Two warning for fire-hit areas including the central tablelands of New South Wales state and southeastern Victoria state.

Australia’s tourism industry accounts for more than 3 per cent of the country’s A$1.95 trillion (US$1.4 trillion) annual economic output. Americans are among the top visitors.

Victorian state capital Melbourne, Australia’s second-biggest city and a major tourist drawcard, was blanketed in hazardous smoke on Tuesday although cooler weather had eased the fire danger.

The city’s air quality dropped to the “worst in the world” overnight as cooler temperatures brought particles in the air close to the ground, a senior state health official said. Residents were advised to stay indoors, bring pets inside and keep windows closed.

Smoke from Australia’s fires has impacted air quality as far away as South America. Soon, the smoke will return to Australian skies having completed a full circuit of the planet.

“The fires in Australia are not just causing devastation locally,” Nasa said in a media release. “The unprecedented conditions that include searing heat combined with historic dryness, have led to the formation of an unusually large number of pyrocumulonimbus events.

“Once in the stratosphere, the smoke can travel thousands of miles from its source, affecting atmospheric conditions globally.”

Scott Morrison roasted for video heralding his bush fire announcements

The Australian Open’s qualifying matches were delayed and practice at Melbourne Park was suspended due to hazardous smoke, tournament organisers said.

The bush fires have affected a number of elite sporting competitions over the Australian summer including soccer, rugby league and cricket, and poor air conditions have raised fears for players’ health at tennis’s first Grand Slam of the year.

At least 180 fires continued to burn across Victoria and New South Wales (NSW) states although widespread rainfall is forecast for fire-hit areas on the east coast from Wednesday.

About 20 bush fires were yet to be contained in NSW, Australia’s most populous state, while in Victoria five fires were at the “Watch and Act” advice warning, one level below emergency status, authorities said.

“I wish I could say this was over, but we have a long way to go,” Lisa Neville, Victoria’s emergency services and police minister told reporters.

Morrison’s conservative government has faced domestic and international criticism for its handling of the fire threat and its response to climate change.

The prime minister signalled on Sunday the government could raise its targets for cuts to greenhouse gas emissions, as long as this did not increase power prices or dent economic growth.

Climate scientists warned that Australia’s fires were a harbinger of what was to come for the rest of the world as the planet warmed due to human activity.

“Temperature conditions in Australia are extreme at the moment but they are what we expect to happen on average in a world of three degrees of global warming,” said Richard Betts, Head of Climate Impacts Research at Britain’s Met Office Hadley Centre. “It brings it home to you what climate change means.”

Additional reporting by Bloomberg