The vehicle collided with another truck parked on the side of the highway where new guard rails were being installed, Saint Gallen cantonal police said.
The Polish truck continued on and struck a small excavator, pushing it 60 metres down a small hillside, police said.
The 36-year-old operator of the excavator was killed, police said.
A 24-year-old worker in the first truck, owned by the special company installing the guard rails, was flown by a Rega emergency services helicopter to hospital for treatment of injuries.
The incident occurred around 10am, near Trübbach, close to the Liechtenstein border.
The driver of the Polish truck, travelling south toward Sargans, appeared to ignore signs shutting off part of the highway for the rail installation, police said.
The accident led to the closure of the highway for a brief period.
Police said the task of removing the Polish truck from crash site was complicated by the fact it came to rest beneath high-voltage electrical transmission wires.
The driver of the truck was unharmed.