Australia’s nuclear safety agency said on Tuesday it had joined a week-long hunt for a tiny radioactive capsule missing in the west of the country that sparked a radiation alert.

The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) is working with the Western Australian government to locate the capsule, it said in a statement.

The capsule, believed to have fallen from a truck, was part of a gauge used to measure the density of iron ore feed which had been entrusted by Rio Tinto Ltd (RIO.AX) to a specialist contractor to transport. The company apologised on Monday for the loss, which could have occurred any time over the past more than two weeks.

“ARPANSA has sent a deployment team with specialised car-mounted and portable detection equipment to support the search of the transport route between the Pilbara region and Perth,” it said in the statement.

“They will be operational from 31 January.”

Authorities are now grappling with the daunting task of searching along the truck’s 1,400 kilometre (870 mile) journey from north of Newman – a small town in the remote Kimberley region – to a storage facility in the northeast suburbs of Perth – a distance longer than the length of Great Britain.

The search is being led by the state’s Department of Fire and Emergency Services alongside radiation experts.

The Australian Nuclear Science and Technology Organisation (ANSTO) has also sent deployment teams of radiation services specialists, and detection and imaging equipment to assist in the search, ARPANSA said.

“ARPANSA is committed to supporting efforts to locate the missing source and protect the community from the harmful effects of radiation.”

Western Australia state emergency officials issued a fresh alert to motorists along Australia’s longest highway on Tuesday to take care when approaching the search party.

“DFES and radiation specialists are searching along Great Northern Highway by driving north and south directions at slow speeds. Take care when approaching and use caution when overtaking.”

The gauge was picked up from Rio Tinto’s Gudai-Darri mine site on Jan. 12. When it was unpacked for inspection on Jan. 25, the gauge was found broken apart, with one of four mounting bolts missing and screws from the gauge also gone.

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 truck.