The bodies of thousands of culled mink have risen to the surface at a mass burial site in western Denmark.
The natural phenomenon occurred at a military training ground near Holstebro at one of the several improvised mass graves across the country.
The carcasses of the animals had risen from the ground under the accumulated pressure of rotting gases, according to the local police.
The bodies are now only covered by a thin layer of lime and very sandy soil, police added.
"There are also problems ... with dead mink being pressed up against the soil surface after they have been dug down," the Ministry for Environment and Agriculture said.
"This is considered to be a temporary problem related to the animals' putrefaction process."
"The National Operating Staff, which has coordinated the mink burials, is aware of the challenges and the dead mink are being covered on an ongoing basis."
Authorities say the mass graves were dug to two and a half metres as recommended, with soil lain on top.
Images of the resurfaced bodies broadcast by public television DR have gone viral on social media, with one Twitter user calling 2020 "the year of the zombie-killing mutant mink".
At the beginning of November, Denmark announced that it was slaughtering its 15 million population of mink because of a COVID-19 mutation that could affect the effectiveness of future vaccines for humans.
The order came after analysis from the Danish health authorities, which had identified cluster variants of the coronavirus in animals.
Denmark's Minister for Agriculture resigned two weeks later when the government found they had no legal basis for the cull order.
Denmark has one of the world's largest populations of mink and breeds the animals for their fur.
More than 10 million minks have already been euthanised, according to the latest report.
The Ministry for Environment and Agriculture has also expressed concern that graves for the killed mink in Holstebro have been dug too close to the Boutrup lake.
Authorities are working with the Danish Environmental Protection Agency (EPA), the Danish Veterinary and Food Administration to ensure that the lake is not polluted with phosphorus and nitrogen from the dead mink.
The EPA had set a distance of 300 metres between the graves and the lake as a precaution, but parts of the burials are less than 200 metres away from the water.
"This must be resolved as soon as possible, and therefore action must be taken immediately," said the new Minister of Food, Agriculture, and Fisheries, Rasmus Prehn, in a statement.
"This is a very unfortunate situation, and it is important that the best possible solution is found quickly, so that the citizens of the area can safely count on the water in the lake being clean."
"It is important to emphasise that this does not spread corona infection," added Nikolaj Veje, director of the Danish Veterinary and Food Administration.
The authorities are discussing whether to install drainage pipes to ensure that any polluting liquid is collected and cleaned away from the lake.
Leif Brøgger, a Holstebro city councillor, has said that the government is "gambling with our nature and using it as a dump".
Denmark says the area will be staffed 24 hours a day until fences are set up around the mass graves