Rio Tinto has apologised for losing a highly radioactive capsule in the Australian outback as authorities scramble to find it.

“We are taking this incident very seriously. We recognise this is clearly very concerning and are sorry for the alarm it has caused in the Western Australian community,” Simon Trott, chief executive of Rio Tinto’s iron ore division, said in a statement.

“As well as fully supporting the relevant authorities, we have launched our own investigation to understand how the capsule was lost in transit.”

The mining giant and Australian authorities now face the daunting task of finding the tiny but potentially deadly 8mm by 6mm unit, which is smaller than a penny.

The small silver cylinder contains caesium-137, a highly radioactive isotope which emits the equivalent of 10 X-rays in an hour.

It fell off the back of a truck while being transported 870 miles (1,400km) from a mine in Newman to a depot in the Perth suburb of Malaga by a specialist contractor on 12 January.

Rio Tinto said it was told by the contractor that the capsule was missing on 25 January.

Authorities suspect vibrations from the truck caused the screws and the bolt to come loose, and the radioactive capsule from the gauge fell out of the package and then out of a gap in the vehicle.

A radiation alert across Western Australia remains in place and authorities have told people to stay at least five metres (16.5ft) away as exposure could cause radiation burns or sickness, though they add that the risk to the general community is relatively low.

The state’s emergency services have set up a hazard management team and have brought in specialist equipment that includes portable radiation detectors. The devices can detect radiation levels across a 20-metre radius, and be used from moving vehicles.

The entire 870-mile route will likely have to be searched until the missing unit is found.

Read more on Sky News:
Woman vanishes while walking her dog
Six children found in abandoned wine cellar
24 star Annie Wersching dies aged 45

Mr Trott said the mining corporation has carried out radiological surveys across the Gudai-Darri mine site where the device had been, as well as the connecting access road.

The task, while akin to finding the proverbial needle in a haystack, is “not impossible” as searchers are equipped with radiation detectors, said Andrew Stuchbery from the department of nuclear physics and accelerator applications at the Australian National University.

“That’s like if you dangled a magnet over a haystack, it’s going to give you more of a chance,” he said.

“If the source just happened to be lying in the middle of the road you might get lucky… It’s quite radioactive so if you get close to it, it will stick out.”