The words 'STOP F1' were written in the skies above Sydney, on Wednesday, amid growing calls for Formula One's season-opening Australian Grand Prix to be scrapped or barred to spectators due to concerns about the coronavirus.
Photographs of the skywriting were widely shared online but it was unclear who was responsible for them.
Formula One organisers have already postponed the Chinese Grand Prix which was scheduled in April, while Bahrain authorities on Sunday said fans would be barred from the second round of the season on March 22.
Australian Grand Prix authorities, on Monday, were adamant that Albert Park would welcome thousands of motor sport fans from Thursday when practice sessions and qualifying commence for lower-profile touring car series.
Australian health authorities are battling to contain community spread of the coronavirus, with infections mounting day by day and several schools forced to close in Melbourne and Sydney.
Australia had recorded 112 cases of the coronavirus as of 11 a.m. local time (0000 GMT) on Wednesday, up from 100 the previous day, the health department said. Three people have died from the disease in the country.
The new coronavirus has infected more than 116,000 people and killed more than 4,000 around the world since it surfaced in China late last year.
More than 300,000 fans attended race week at Albert Park last year, according to organsiers' estimates.
With a prominent art festival in Australia's southern Tasmania state and other local events cancelled in recent days, Australian media pundits have queried the safety of thousands of fans flocking to Albert Park.
"In the real world, the Indian Wells tennis tournament in the US has been cancelled, the Socceroos World Cup qualifiers have been postponed, major club matches in Italy are being played behind closed doors, and the World Cup skiing finals in Cortina d’Ampezzo have been scratched altogether," Greg Baum wrote in Melbourne daily The Age on Tuesday.
"In the Melbourne Grand Prix world, it’s see you in the champagne tent."