News of the variant triggered alarm and a sell-off last week in financial markets, as countries clamped on new curbs for fear it could resist vaccinations and upend a nascent economic re-opening after a two-year global pandemic.
The World Health Organisation, WHO, warned that deciding the severity level of Omicron, identified first in South Africa, could take "days to several weeks" in the absence of information that its symptoms differed from those of other variants.
Asian markets and oil prices regained some composure as investors settled in for a few weeks of uncertainty as they wait for more details.
Australia will review plans to re-open to skilled migrants and students from Dec. 1, Prime Minister Scott Morrison said on Monday, while adding it was a "bit too early" to reinstate two-week mandatory hotel quarantine for foreign travellers.
"So we just take this one step at a time, get the best information, make calm, sensible decisions," Morrison told broadcaster Nine News.
A national security panel will meet later in the day to assess border relaxations due from Wednesday, he added, with leaders of all states and territories to meet by Tuesday.
He called for calm as the severity, transmissibility and vaccine resistance of Omicron had not been determined, echoing remarks by the WHO, which dubbed it a "variant of concern".
Potentially more contagious than previous variants, Omicron has now been detected in Australia, Belgium, Botswana, Britain, Canada, Denmark, France, Germany, Hong Kong, Israel, Italy, the Netherlands and South Africa.
Symptoms of Omicron were so far mild and could be treated at home, a South African doctor, one of the first to suspect a different variant, has said.
Countries from Indonesia to Saudi Arabia have imposed travel curbs for visitors from southern Africa to limit the spread.
Singapore has deferred the start of vaccinated travel lanes with some Middle Eastern countries, such as Qatar, Saudi Arabia and the United Arab Emirates, given "their proximity as transport nodes to the affected countries", its health ministry said.
Britain said it would call an urgent meeting of G7 health ministers on Monday.
In the most far-reaching effort against the variant, Israel is to ban the entry of foreigners and re-introduce counter-terrorism phone-tracking technology, it has said.
South Africa has denounced the measures as unfair and potentially harmful to the economy, saying it was being punished for its scientific ability to identify variants early.
"The prohibition of travel is not informed by science, nor will it be effective in preventing the spread of this variant," President Cyril Ramaphosa said on Sunday.
"The only thing (it) ... will do is to further damage the economies of the affected countries and undermine their ability to respond."
President Joe Biden will give an update on the variant and the US response on Monday, the White House said in a statement.
It will take about two weeks to get definitive information about the transmissibility and other features of Omicron, Dr Anthony Fauci, the top US infectious diseases official, has told Biden, it added.
Fauci believes existing vaccines "are likely to provide a degree of protection against severe cases of COVID", the White House said.