Nicola Sturgeon has warned Scotland faces a "tsunami of infection" due to the Omicron variant of coronavirus.
The First Minister said reported cases of the new strain - which was first discovered in southern Africa last month - were doubling roughly every two days.
The SNP leader said early data suggested booster vaccines were "doubly important".
But she added experts did not yet know whether Omicron caused a higher risk of serious illness.
Scots will now be expected to self-isolate at home for 10 days if any of their household reports a positive covid test.
And Sturgeon repeated a plea from public health experts that people should "defer" work Christmas parties.
Speaking at a media briefing in Edinburgh, she said: "Omicron right now is rising exponentially, indeed what we are seeing in the data just now is perhaps the fastest exponential growth that we have seen in this pandemic so far.”
She added: “If that continues, and we have no reason, at this stage, to believe that it won’t, Omicron is going to very quickly overtake Delta as the dominant strain in Scotland.
“Indeed, I think we can now say with some confidence that we expect it to overtake Delta within days, not weeks – we estimate this could be as early as the very beginning of next week.”
A Scottish Government evidence paper published moments before Sturgeon started speaking warned cases of Omicron would likely sharply rise in the coming days.
It revealed that hundreds of potential cases of the new variant are currently under investigation across Scotland.
It added: “It is highly probable that Omicron will outcompete Delta and become the dominant variant within Scotland very quickly, with the potential to cause high case numbers”
"The rapid rise in Omicron infections could put significant additional pressure on hospitals and other health and care services, close to the point in the winter when they are already likely to be at peak pressure."
Sturgeon stressed that people should still get jabbed although evidence suggests Omicron can evade some immunity conferred by vaccines.
She added: “Based on preliminary laboratory trials, the best evidence suggests it can evade to some extent the immunity conferred by vaccination.
“Now, and I want to triple underline this point, that does not mean that the vaccines will not significantly help us – being less effective is not the same, nowhere near the same as vaccines being ineffective and booster doses in particular will help retain a higher level of vaccine efficiency.”
Jackie Baillie, Scottish Labour's health spokeswoman, said: “This is a stark warning about what may lie ahead.
“We are right to be cautious when there is a real risk of the NHS being overwhelmed.
“Every effort must be made to help people, businesses and public services get through this challenging period.
“We need to ramp up efforts to get everyone fully vaccinated as a matter of urgency, and if businesses are going to be affected it is absolutely vital that they get the support they need.
"Scottish Labour are clear that public health must be protected, and our response must be firmly rooted in the evidence.”
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