Black ice is treacherous because it is often invisible but makes the road surface extremely slippery. It forms when the road surface is cold and damp at temperatures around zero degrees Celsius, the Swedish Transport Administration says in a press release.
The warning applies to large parts of central and western Sweden, but other parts of the country may also be affected.
People across most of the country must now prepare for icy conditions, says Daniel Mossberg, a press spokesperson for the Swedish Transport Administration.
To reduce the risk of accidents, the Swedish Transport Administration urges road users to accelerate and brake gently and switch to winter tires.