Authorities say the radioactive substance inside the radiography device could spread dangerous contamination if dismantled improperly.
There are also fears it could be used as part of a weapon - a so-called dirty bomb - if it fell into the wrong hands.
Authorities have confirmed the device is missing but have insisted that "everything is under control".
The missing object is used in industrial radiography - it belonged to a firm that does tests, calibrations and inspections for oil and gas companies and other heavy industry firms.
The 23kg (50lbs) large metal tube with a carrying handle had reportedly been used to spot cracks in metal.
It contains the radioactive isotope iridium-192 which can cause radiation exposure or be used as a weapon if combined with a conventional explosive device.
Whether or not the missing iridium can indeed be used for a so-called dirty bomb depends on how much of it was inside the device.
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