A British mechanic was told he had tested positive for the coronavirus at 9pm. A little more than an hour later, his McLaren team informed F1 and the FIA that they were pulling the plug on their participation this weekend.
The individual remains in quarantine at the team's hotel in Melbourne. It is understood that at least a dozen other McLaren staff are in self-isolation after coming into contact with the individual who arrived from England earlier this week. They are showing no symptoms related to the disease.
In all, nine people connected with the sport, none of whom are from Hamilton's Mercedes team, have been tested for the virus, seven of which have been negative, one positive, and one still awaiting their results.
"McLaren Racing has confirmed this evening in Melbourne that it has withdrawn from the 2020 Formula One Australian Grand Prix, following the positive test of a team member for the coronavirus," a statement from the British team read.
"The team member was tested and self-isolated as soon as they started to show symptoms and will now be treated by local healthcare authorities.
"The team has prepared for this eventuality and has ongoing support in place for its employee who will now enter a period of quarantine."
McLaren will now take direction from the local authorities regarding their next steps.
Earlier on Thursday, six-time world champion Hamilton attacked F1's decision to stage the Melbourne race.
"I am really very, very surprised that we are here," he said during the official press conference to preview Sunday's event. "For me, it is shocking that we are sitting in this room.
"It seems like the rest of the world is reacting, probably a little bit late, but we have seen [US president] Donald Trump shut down the borders from Europe to the US, the NBA has been suspended, yet Formula One continues to go on."
Asked why he thought the sport's chiefs and its governing body, the FIA, had pushed ahead with the event, Hamilton, 35, said: "Cash is king. I don't feel like I should shy away from my opinion.
"The fact is we are here and I just urge everyone to be as careful as you can be in terms of touching doors and surfaces. For the fans, I hope they take precautions, too.
"I was walking through the paddock and saw everything going ahead as normal as if it is a normal day, but I really don't think it is. I saw Sir Jackie Stewart in the lift this morning looking fit, healthy and well, and other elderly people, too. I hope the fans stay safe and we don't see any fatalities or anything come out in the future."
Four-time world champion Sebastian Vettel, a director for the Grand Prix Drivers' Association, said that the grid could refuse to race if it was confirmed a team member had been infected.
"If it was to go that far, for sure you pull the handbrake [on the race]," said Vettel, 32.
"We are a group of 20 guys and we got together over the years in various circumstances and I think we share common opinion on big decisions and that would be a very, very big decision.
"We would be mature enough to look after ourselves and pull the handbrake in that case."
Next weekend's Bahrain Grand Prix, which was already set to be staged behind closed doors, now looks unlikely to take place, while the inaugural race in Vietnam, scheduled for April 5, is also under major threat. Following the postponement of the Chinese Grand Prix, the season could now start in Holland on May 3, but that is also subject to change.
HOW THE DRIVERS ARE DEALING
Australia has reported 150 cases of coronavirus so far, including among fans who attended the women's T20 Cricket World Cup final and a Super Rugby match, both in Melbourne last week.
European countries that are home to many of the F1 teams and journalists at the grand prix have had far more cases.
Despite concerns, fans flocked to Albert Park on Thursday for a Supercars qualifying session.
"I'm not worried, I'm washing my hands and that's the best thing to do," said spectator Robert Clarke as he used a hand-sanitiser station.
The first F1 practice sessions are due to start on Friday.
In an attempt to limit interaction between drivers and fans, autograph sessions have been replaced by question and answer interviews, with selfies banned.
Media events have also been hit with Renault's Ricciardo and Esteban Ocon "excused" from a press conference Wednesday, and an exclusion zone was enforced around Max Verstappen and Alex Albon at a Red Bull function.
Ocon was spotted wearing a mask in the paddock on Thursday, while teams scrapped all-in TV interviews, where media are tightly packed around the drivers, for the duration of the weekend.
The coronavirus has already hurt the sport with April's Chinese Grand Prix postponed, while the second race of the year in Bahrain will be held without spectators.
The Australian Grand Prix Corporation said it was working closely with health authorities to take additional precautions at Albert Park, including having hand sanitisers at public areas and corporate facilities.
Cleaning and disinfection programmes have been increased and protocols implemented to respond to any suspected COVID-19 cases.
Over the weekend, the FIA said it was establishing a "crisis cell" to meet every two days to monitor the global threat posed by the virus.
