A total of five people were killed in a 51-vehicle pile-up on the highway linking this capital to Chile's main seaport, the Carabineros militarized police force said.

The fatalities were listed as four adults and an 11-year-old boy identified as Bryan Gomez Vargas, who was found inside a truck left mangled on the side of the road.

Another 40 people were injured in Wednesday's pile-up, the report said.

Low visibility due to fog and the burning of nearby cropland was blamed for the accident, which occurred near Casablanca, a town in Valparaiso province some 80 kilometers (50 miles) from Santiago.

A total of 51 vehicles - including 23 trucks and 11 buses - were involved in the collision on the Autopista del Sur, which links Santiago and the San Antonio port, Valparaiso emergency management office chief Guillermo de la Maza said.

Health Minister Jaime Mañalich, who arrived on the scene shortly after the accident, when the preliminary death toll was four, had told reporters that it could rise because a number of people were trapped inside their vehicles.

Firefighters and a Carabineros air police unit were involved in the effort to remove victims to safety and transport them to hospitals in the coastal cities of Valparaiso and Viña del Mar.