A legally-enforceable stay-at-home order now applies for all of January in all areas currently under Level 4 restrictions - mainland Scotland and Skye.
People will only be permitted to leave their home for an "essential purpose", such as essential shopping, caring for someone or if they are part of an extended household.
Yesterday, Nicola Sturgeon said Scotland is in “a race between the vaccine and the virus”.
The First Minister stressed the need to act "quickly and decisively" as she said without new measures being introduced hospitals could run out of capacity to deal with coronavirus patients in three to four weeks.In addition to this, schools will be closed to most pupils until February 1 at the earliest - meaning an additional two weeks of home learning for youngsters.
Ms Sturgeon tweeted late on Monday night: “Being back in lockdown is really hard to take for everyone, but it is necessary to slow down this new strain of the virus while we get people vaccinated.
“Please – for you own safety, that of your loved ones and of the whole country: Stay at Home, Protect the NHS and Save Lives.”
The First Minister said yesterday soaring case numbers of Covid-19 and the modelling of the spread of the virus suggested that without stringent new restrictions NHS capacity could be breached within three weeks.
She said prevarication or delay in dealing with the virus “almost always makes things worse not better” and that to ensure Scotland did not see the level of cases currently being experienced in London the government needed to “act quickly”.
Ms Sturgeon said Monday’s case numbers – 1,905 new cases, with 15 per cent of tests being positive – “illustrated the severity and urgency of the situation”.
The lockdown restrictions are similar to those introduced in March at the start of the pandemic.
Ms Sturgeon said: “This means it will only be permissible to leave home for an essential purpose. This will include, for example, caring responsibilities, essential shopping, exercise and being part of an extended household.
“In addition, anyone who is able to work from home must do so. It will only be a reasonable excuse to leave your home to go to work, if that work cannot be done from home.”
It is understood the Covid threat level – which is decided by the Joint Biosecurity Centre that includes the UK's four chief medical officers – is being moved up to five, the highest level, for the UK.
Addressing MSPs in the Scottish Parliament, Ms Sturgeon said: “There have been two significant game changers in our fight against this virus.
“One, the approval of vaccines, is hugely positive and offers us the way out of this pandemic. But the other – the new faster spreading variant of the virus – is a massive blow.
“Possibly the most simple way of explaining the challenge we face right now is to compare it to a race. In one lane we have vaccines – our job is to make sure they run as fast as possible. That’s why the government will be doing everything we can to vaccinate people as quickly as possible.
“But in the other lane is the virus, which – as a result of this new variant – has just learned to run much faster and has most definitely picked up pace in the last couple of weeks.
"To ensure that the vaccine wins the race, it is essential to speed up vaccination as far as possible. But to give it the time it needs to get ahead, we must also slow the virus down.
“And because it is now spreading faster, that means even tougher restrictions are necessary.”
On schools Ms Sturgeon said: “I can confirm … we will keep schools closed to the majority of pupils until February 1. We will review this again in mid January.
"The change will apply to all pupils – except vulnerable children, and children of key workers. And it includes nursery schools, as well as primary and secondary schools.”
She said while the evidence “makes clear” that schools have been “low-risk environments for Covid”, the high levels of community transmission and the uncertainty of the impact of the new variant of the virus on young people meant schools had to close.
However, there will be “ongoing work on testing in schools and discussions about when, in the context of the overall programme, it will be possible to vaccinate school staff”.
The new restrictions also mean that people who were previously shielding because of other health conditions, and who cannot work from home, should not go into work at all.
However, unlike the lockdown last year, the frequency of outdoor exercise is not being limited, to allow people to “get outdoors for fresh air and exercise as much as possible”, though the rules will change.
From Tuesday, a maximum of two people from up to two households will be able to meet outdoors, although children aged 11 and under will not be included in that limit.
Places of worship will also close, with the exception of conducting a funeral or wedding, though the numbers able to attend such services have been reduced.
Opposition parties welcomed the announcement in the light of rising cases, but stressed more support would be needed for working parents and businesses.
Ruth Davidson, Holyrood leader of the Scottish Conservatives, said the announcement showed the need to have a “comprehensive” test and trace system in place and questioned why the full capacity of 65,000 tests a day wasn't being used.
Ms Sturgeon said the capacity and demand would not be equal as testing was dependent on people with symptoms coming forward.
Ms Davidson said: “It's impossible to know if we’re winning the race between vaccine and virus, if we only show the daily infection figures without daily vaccination figures.
"Can she commit to publishing not just national vaccination figures, but numbers by health board and can she tell us when everyone in the over-80 cohort will receive their letter with vaccination details?”
Ms Sturgeon said the government was “intending to break down the weekly publication of the numbers vaccinated into categories and we will consider doing that by health board as well”.
She said: “I’m mindful of not putting too many burdens of data collection on people we’re expecting to undertake this huge logistical challenge.
"The vaccine programme is still in its early stage, but we’ve vaccinated more than 100,000 people and we will continue to focus on accelerating that as much as possible, though it is largely constrained by supply. We're not yet clear on what supplies we can expect beyond January.”
Scottish Labour leader Richard Leonard said the government needed to encourage businesses to furlough working parents who need time off to support their children while schools were closed.
He also called for £500 self-isolation support payments to be extended to a greater number of low-income workers as less than a quarter of applications had been successful.
“The issue here is not just whether schools and school buildings are open or not,” he said.
"It is how much preparation has been made by her government for the continuation of our children’s education. It is about whether the remote learning materials which were promised back in July are ready now six months later.
“It is about how much support there is for working parents, what the plan for them? For example, does the First Minister have a plan to encourage all businesses to furlough all working parents to take the time off to support their children.”
Ms Sturgeon said: “We have taken significant steps around online learning. The national e-learning offer, a collaborative programme, has already helped improve the options available to schools, with provision for live remote learning, recorded lessons and online digital learning.
"We will continue to look at that on an ongoing basis, but fundamentally the priority here in getting transmission down again is to keep the period of schools being closed as short as possible.
"We will be discussing, led by the Economy Secretary and starting today, with business organisations the expectations of businesses to do everything they can to support workers to work from home and support workers with childcare responsibilities. We're at a stage here where we need to have national collective endeavour to overcome this severe challenge we face and I know businesses will play their full part in that.”
Ms Sturgeon said there would be a later announcement on financial and other types of support for businesses and low-income families.
Scottish Liberal Democrat Leader Willie Rennie asked if “given the threat of the virus is greater with age” there would be an earlier return of nurseries and primary schools compared to secondary schools?
Ms Sturgeon replied: “When it comes to getting schools back, it won’t necessarily be a binary, open or closed decision. One thing we will look at is if primary schools could come back before we felt it safe to bring secondary schools back, all these things are very much under consideration."