Work by Scottish Power at Anderston Tower, in Motherwell, is thought to have disturbed asbestos.
North Lanarkshire Council evacuated the building as a precautionary measure.
Council workers carried out air quality testing and decided to remove tenants for the night to allow staff to carry out investigations.
A spokesman for North Lanarkshire Council said: "Initial testing has shown a number of positive results within the building.
"While we do not believe that there is any immediate risk to health, the wellbeing of our tenants is our priority."