Two pontoons involved in a mysterious military test explosion in northern Russia last month have been left unguarded on the shore near a village despite high radiation readings, according to a video.

Radiation levels spiked in the Arkhangelsk region and at least five employees of state nuclear concern Rosatom were killed when a “liquid-fuel reactive propulsion system” exploded during testing near the village of Nyonoksa on August 8.

Rosatom said the blast occurred during work on “isotope power sources” for the engine, which commentators have speculated was for either the Burevestnik nuclear-powered cruise missile or a space rocket.

The authorities have claimed the accident posed no risk to residents' health, even though doctors at a regional hospital said they were unwittingly exposed to radiation when treating patients from the site. Caesium-137 was later found in the body of one of the doctors.

Satellite imagery revealed that two floating platforms were swept to the shore of the Dvina Bay in the days after the accident. Locals posted a photograph of the platforms, one of which was severely damaged, on social media, warning others to stay away with the caption “this is what death looks like”.

On Monday, the Belomorkanal news site uploaded a YouTube video of men taking radiation readings near the platforms on a beach near the mouth of the Verkhovka river.