If Macau was proud of its Covid-free record for more than 400 days, the alarm over a family cluster reveals how shaky such confidence can be.
The entire enclave is in a state of high alert. Although the Macau government called it a "state of immediate prevention," it is a de facto state of emergency.
Since the announcement, there have been reports of panic buying as residents snapped up food and toilet rolls overnight.
As far as the pandemic is concerned, Hong Kong is still one of the safest places in the world.
Although its figures may not be as outstanding as those of Macau, it has been some time since panic buying was last reported here.
Bubbles are bound to burst but, if rebuilding confidence depends on zero cases, this would be too brittle as no place can be permanently isolated from the outside world.
In the latest incident in Macau, the chain of infection was traced to a girl who had been to Xian on an exchange program.
She left home to go to Zhuhai in July, then took a flight to Xian. It is believed she was infected during the flight and returned home to infect her family members.
As we all know, the mainland has maintained a stringent set of measures to keep Covid at bay, but it is still occurring.
In this particular case, the Macau girl was infected on a domestic flight in the mainland.
There is no doubt that the only lasting solution is to vaccinate as many residents as possible. All others are only stop-gap measures.
After Macau Chief Executive Ho Iat-seng stepped up the local emergency to shut down nearly all entertainment venues and tightened pre-departure negative Covid-test requirements - as demanded by Zhuhai - Hong Kong Chief Executive Carrie Lam Cheng Yuet-ngor finally had a chance to respond forcefully to Macau's emergency call.
Maybe Lam should be forgiven for quickly expelling Macau from the "Return2HK" scheme.
Yes, her swift announcement to exclude Macau from the scheme has won her some applause. However, the sudden suspension of Macau's part that would have otherwise allowed Hongkongers to go home without having to isolate is causing a great deal of stress.
Arguably, the move could be considered overkill.
Hopes of greater convenience in Hong Kong-mainland travel are now more far-fetched.
When even a handful of cases in Macau has caused the bubble to burst, reports of Covid spreading to at least 17 mainland provinces is highly alarming.
When it comes to the pandemic, there is nothing that Hong Kong, Macau and the mainland need to compete over - but there is plenty for them to cooperate over for the good of all.
In a sense, the fact that Macau's population is less than one tenth of Hong Kong's should make it possible for the enclave to conduct population-wide tests within a few days.
But at least one Macau legislator decried the ensuing chaos over the tests.
Clearly, given Macau's small size, Ho could have done better.