Thieves have stolen a cargo of depleted uranium (DU) from a warehouse in Essex.
Depleted uranium is mildly radioactive
The DU was in a white Citroen Berlingo van which they stole from a warehouse in Aveley.
Essex Police stressed the substance is not particularly dangerous to the public.
The alarm was raised just before 1400 BST on Sunday when staff at a warehouse on the Purfleet Industrial Estate noticed the white van was missing.
The company, which has not been named, uses the product to help with the inspection of industrial pipes.
Depleted uranium is mildly radioactive in its solid form, and poses little cause for concern.
But it is a very heavy substance, 1.7 times denser than lead, and is commonly used on the tips of artillery shells to punch through heavy armour.
Both the US and the UK acknowledge that the DU dust can be dangerous if it is inhaled.
Many veterans from the Gulf and Kosovan wars believe that depleted uranium has made them seriously ill.