The huge pile-up occurred in dense fog and icy conditions, the morning after Switzerland's coldest night of the winter so far.
The junction between Reichenburg and Bilten remains closed and a rescue operation is underway involving several ambulances and air rescue service Rega, said police.
Ice and snow in some parts of the country has caused several other accidents in the past few days.
On Wednesday evening three young people died when two cars collided head-on near Densbüren in the canton of Aargau.
The driver of one of the vehicles is believed to have lost control of his car coming down a hill in wintry conditions, said Aargau police.
A 19-year-old occupant of the car died at the scene, while two others succumbed to their injuries later in hospital.