Video report by ITV News Scotland Correspondent Peter Smith
Schools in Scotland will also remain closed to most pupils until February at the earliest to help contain the spread of coronavirus, Ms Sturgeon confirmed in the Scottish Parliament.
Under the new rules, people are being told to stay at home, with exceptions for exercise, essential journeys and work purposes if you cannot work from home.
Addressing MSPs in Holyrood, Ms Sturgeon said: "I am now more concerned about the situation now than I have ever been since March.
"The situation in the NHS is fragile and it is getting more challenging," she said.
Watch the full announcement:
Ms Sturgeon added the new lockdown will be similar to March with the "fundamental advice for everyone to stay at home" and will be enforced as a law from midnight.
Ms Sturgeon said the new restrictions will be enforced "until at least the end of the month" - but added it could be longer than January.
Without intervention, Ms Sturgeon has said, the NHS in Scotland may become overwhelmed in the coming weeks.
According to modelling by the Scottish Government, the first minister told MSPs, taking no action could see Covid-19 capacity in hospitals overrun within "three or four weeks".
Ms Sturgeon said: "We have an opportunity in Scotland to avert the situation here deteriorating to that extent. But we must act quickly."
The first minister told MSPs: "The advice of our clinical advisers is clear that the increased transmissibility of the new variant means that the current Level 4 measures may not be sufficient to bring the R number back below one.
"It is essential that we further limit interaction between different households to stem the spread and bring the situation back under control, while we vaccinate more people.
"In short, we must return for a period to a situation much closer to the lockdown of last March."
Announcing a raft of changes to coronavirus restrictions, including a new period of lockdown for areas in Level 4, Ms Sturgeon said a period of home learning would drive down transmission rates.
She also said the scientific community was not clear on the impact of the new variant of Covid-19 on young people.
Ms Sturgeon said: "Just as the last places we ever want to close are schools and nurseries, so it is the case that schools and nurseries will be the first places we want to reopen as we re-emerge from this latest lockdown - they remain our priority."
The first minister's statement comes as a further 1,905 people in Scotland have tested positive for Covid-19 - 15% of the 13,810 tests carried out on Sunday.
No new deaths have been reported on Monday but Ms Sturgeon has said 289 deaths have been recorded in the daily figures since she last updated Parliament.