Restrictions have come into force in three council areas, including the city of Glasgow, after days of surging coronavirus cases.
From midnight, people in Glasgow, East Renfrewshire and West Dunbartonshire cannot host or visit other households indoors for at least two weeks.
Members of different households can continue to meet outdoors, including gardens and venues such as pubs or restaurants, provided social distancing is maintained.
The First Minister made the announcement after chairing a meeting of the Scottish Government Resilience Committee (SGoRR) on Tuesday afternoon.
The restrictions follow more than 400 new Covid-19 infections recorded in Scotland in the last three days, with 174 found in the Greater Glasgow and Clyde health board area.
Anyone living in the three council areas who is a close contact of someone who has tested positive for coronavirus must self-isolate for 14 days along with the rest of their household.
Indoor visits to hospitals and care homes will be limited to essential visits, while outdoor visits to care homes will be restricted to three people from a maximum of two households, in line with current guidance.
Extended households and people providing care and support, such as caring for family members or delivering shopping can continue to meet indoors with enhanced hygiene measures in place.
People who have been shielding in the affected areas have been asked to be vigilant.
Schools and nurseries will remain open, and plans for the opening of colleges and universities remain in place.
Nicola Sturgeon said: “The rise in new Covid-19 cases in all three of these local authority areas is of significant concern and these figures remind us all that the virus has not gone away. We are at a stage of this pandemic where we must all act with extreme caution.
“Following discussions with local public health officials and local authorities, it is necessary to ask people in Glasgow, West Dunbartonshire and East Renfrewshire to limit their contact with other households.
“People living in these areas should not meet with other households in indoor household settings for at least two weeks, except where they are providing essential care and support, or have formed an extended household.
“People can continue to meet other households outside and in other settings but I would ask everyone to be extra vigilant, to follow all guidance and to isolate and book a test if they have any symptoms.
“Above all, I want to emphasise that getting a test – and even getting a negative result – is not a substitute for self-isolating. If you have symptoms, or if you are contacted by our Test and Protect team and told to do so, you will need to self-isolate.
“I understand this will not be welcome news for people living in Glasgow, East Renfrewshire and West Dunbartonshire but it is necessary to help us limit the spread of Covid-19.
“Acting now gives us the time and the space to protect people and get more control over the virus.”