Smoke from the bushfires ravaging Australia will return there after circling the Earth, NASA has said.
Huge infernos have raged along the nation’s east coast for months and the smoke has already reached South America, resulting in hazy skies over Chile and Argentina, 4,000 miles (6437 km) away.
“The smoke is expected to make at least one full circuit around the globe, returning once again to the skies over Australia,” the US space agency said in a statement.
“Over the past week, Nasa satellites have observed an extraordinary amount of smoke injected into the atmosphere from the Australian fires and its subsequent eastward dispersal.”
At least 28 people have been killed and more than 2,500 homes destroyed in one of Australia’s worst bushfire seasons on record.
Forests and farmland the size of Bulgaria have been razed by the blazes, which began in September.
The warning comes as concerns increase that the Australian Open tennis tournament in Melbourne, due to start on Monday, will be affected by the poor air quality.
On Tuesday, Slovenian player Dalila Jakupovic was forced to retire from her qualifying match after collapsing because she “couldn’t breathe”.
The world number 180 was leading her first-round tie against Switzerland’s Stefanie Voegele when she dropped to her knees with a coughing spell.
Ms Jakupovic said: “I was really scared that I would collapse. I don’t have asthma and never had breathing problems. I actually like heat.
“The physio came again and I thought it would be better. But the points were a bit longer and I just couldn’t breathe anymore and I just fell on the floor.”
Jakupovic said it was “not fair” that officials asked players to take the court in those conditions.
“It’s not healthy for us. I was surprised, I thought we would not be playing today but we don’t have much choice.”
Tuesday’s practice session at Melbourne Park was suspended and former world number one Maria Sharapova’s warm-up match was called off.
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.