The tiny radioactive capsule that sparked a massive hunt has been found just south of Newman in a remote area of Western Australia.

Officials on Wednesday afternoon told a press conference in Perth that the 8mm by 6mm ceramic capsule, which is smaller than a 10-cent piece, was found about two metres off the side of the road on the Great Northern Highway at 11.13am, local time.

Specialist equipment used in the search detected the capsule when it was travelling in a vehicle at 70km/h.

The Australian Radiation Protection and Nuclear Safety Agency said on Tuesday it had sent a team with specialised car-mounted and portable detection equipment to join the search.

The capsule, which was described as posing a significant public health risk as it contains Caesium-137, was placed in a lead container and taken to Perth.

It will be stored in a secure location in Newman before being transported to a Perth health facility.

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Department of Fire and Emergency Services Commissioner Darren Klemm said the capsule was found intact in a remote area.

A 20-metre hot zone has been created, with the site to be surveyed on Thursday to ensure there was no contamination.

Search crews had spent six days scouring a 1400-kilometre route amid warnings the Caesium-137 in the capsule could cause radiation burns or sickness if handled and potentially dangerous levels of radiation with prolonged exposure.

Emergency Services Minister Stephen Dawson said the discovery was remarkable considering the scope of the search.

“This is an extraordinary result … they have quite literally found the needle in the haystack,” he told reporters.

A government investigation has been launched into the incident and a report will be provided to the health minister.

Defence officials are verifying the identification of the capsule.

Chief health officer Andy Robertson said the capsule did not appear to have moved and no injuries had been reported.

The capsule was lost on January 12, when a truck left Rio Tinto’s Gudai-Darri iron ore mine in the Pilbara region and drove 1400 kilometres south to Perth, arriving on January 16.

On January 25, it was discovered the truck had lost the capsule containing a highly radioactive substance, used in a radiation gauge on the mine site.

The capsule, which contains Caesium-137, will be placed in a lead container and taken to Perth.

The capsule contains Caesium-137, a radioactive isotope which spits out electrons (or beta radiation) and high-energy photons (or gamma radiation).

Caesium-137 is used in some cancer treatments, for measuring the thickness of metal or the flow of liquids, and – as in this case, reportedly – for calibrating radiation gauges.

About 100 personnel including the Australian Defence Force, Australian Nuclear Science and Technology Organisation, Australian Radiation Protection and Nuclear Safety Agency were among those involved in the search.

-with AAP