Several train wagons have derailed in South Australia, affecting key freight services connecting the country.

The derailment of a freight train on a key section of railway in South Australia is affecting all transcontinental train services as heatwave conditions in the area impact the pace of recovery works.

A freight train has come to a halt after eight of its carriages rolled off of the tracks next to the Augusta Highway near Mambray Creek leading to the rail line to be blocked.