The accident occurred shortly before midday on an E4 motorway bridge just northeast of Helsingborg, the Swedish news agency TT reported.
The E4 was closed in both directions so rescue crews could work.
"Several people are stuck in their cars," said chief fire fighter Christer Haraldsson. "We have a large number of ambulances on their way and we are sending a bus to evacuate the area."
A news photographer at the scene said the accident "stretches as far as the eye can see" and involves vehicles on both sides of the motorway.
Police blamed the crash on slippery road conditions and a dense fog that blanketed the area.