Rio Tinto says it is taking the loss of a radioactive piece of equipment smaller than a 10 cent piece between its Western Australia mine site and Perth "very seriously".
The company has launched an internal investigation into how the item went missing over a 1400-kilometre stretch of road.
It comes as authorities also launched their own probe and began to comb parts of the roads for the capsule.
The capsule is understood to have fallen from a truck of a contractor hired to transport the device after leaving the site in Newman, in the Pilbara, on January 10. The truck arrived at a Perth depot in Malaga on January 16.
"We recognise this is clearly very concerning and are sorry for the alarm it has caused in the Western Australian community," Rio Tinto's Iron Ore chief executive Simon Trott said on Sunday.
"As well as fully supporting the relevant authorities, we have launched our own investigation to understand how the capsule was lost in transit."
WA emergency services have called on other states and the federal government for support finding the capsule as they lack the equipment to search for the device.
The search has involved people scanning for radiation levels from the device along roads used by the trucks, with authorities flagging the entire 1400km route might have to be searched.
The silver 8mm by 6mm capsule is a caesium 137 ceramic source commonly used in radiation gauges.
It emits dangerous amounts of radiation, which is the equivalent of receiving 10 X-rays in an hour.
It could cause skin burns and prolonged exposure could cause cancer. People have been warned it could have unknowingly become lodged in their car's tyres.
Australian Associated Press