Poland has started logging in the ancient Białowieża forest, which includes some of Europe’s last primeval woodland, despite fierce protests from environmental groups battling to save the world heritage site.

“The operation began today,” national forest director Konrad Tomaszewski said of the plan to harvest wood from non-protected areas of one of the last vestiges of the immense forest that once stretched across Europe.

He said the goals were to stop forest degradation by combating what the environment ministry says is a spruce bark beetle infestation, and protect tourists and rangers from harm by cutting down trees that risk falling on trails.

However, the only published inventory shows that nearly half of the trees earmarked for logging may be non-spruce varieties, which have been unaffected by the beetle outbreak. And environmental campaigners warn that the tree chopping will destroy an ecosystem unspoiled for more than 10,000 years that is home to the continent’s largest mammal, the European bison, and its tallest trees.

“We’re calling on the European commission to intervene before the Polish government allows for the irreversible destruction of the Białowieża forest,” said Greenpeace Poland activist Katarzyna Jagiełło.

“We need to halt this [bark beetle] disease in its tracks,” said Poland’s environment minister Jan Szyszko. “We need to ensure that there is a healthy logging of trees, something that is planned. We only want to fell an area of 188,000 cubic metres. We want to protect priority habitats for the EU. We are trying to improve and correct the situation.”

Campaigners have taken issue with the government rationale for the project, saying the beetle’s presence does not pose any threat to the forest’s ecosystem.

“The minister does not understand that this insect is a frequent and natural visitor, that it has always existed and the forest has managed to survive,” Jagiełło said.

The forest is home to Europe’s tallest trees. Photograph: Łukasz Mazurek/WildPoland.com

Greenpeace said its patrols had come across the first signs of logging overnight on Tuesday and Wednesday morning between the eastern town of Hajnówka on the border with Belarus and the village of Białowieża to the north.

The Białowieża project is the latest action by Poland’s new rightwing government to draw criticism at home and abroad, including an overhaul of the country’s top court and legislation strengthening state control over public broadcasters.

The environment ministry has said loggers will chop down more than 180,000 cubic metres (6.4m cubic feet) of wood from non-protected areas of the forest over a decade, dwarfing previous plans to harvest 40,000 cubic metres over the same period.

Last month, seven groups – including Greenpeace Poland and the Polish branch of WWF – lodged a complaint with the European commission over the logging.

EU environment spokeswoman Iris Petsa said at the time that the commission was “concerned” about the project.

Białowieża, which was designated a Unesco World Heritage site in 1979, covers about 150,000ha (370,650 acres) in Poland and Belarus.

It is home to 20,000 animal species, including 250 types of bird and hundreds of European bison, plus firs towering 50 metres (160ft) high and oaks and ashes of 40 metres.

In Belarus the entire forest is protected as a nature park, but only part of the Polish section is protected.

Warsaw has vowed that the logging would not take place in the protected areas.

Tomaszewski said forest management would refrain from logging in two “reference areas” to allow “nature to fend for itself”.

Szyszko said the operation was aimed at protecting sites of great heritage value that are part of Natura 2000, an EU network set up to preserve Europe’s most valuable and threatened species and habitats.

The Białowieża forest is the last remaining primeval forest in European lowlands. Photograph: David Levene/The Guardian

But the non-profit environmental law organisation ClientEarth said it was “surprised that Szyszko had invoked EU law to justify the logging”.

“The decision to multiply the cutting is not compliant with EU law because it was not preceded by an environmental impact study of the species and the protected sites,” said ClientEarth lawyer Agata Szafraniuk.

“A case before the EU court is unfortunately becoming more and more likely.”

A delegation from Unesco is due to visit Białowieża between 4 and 8 June to assess the situation.

Luc Bas, the director of the International Union for the Conservation of Nature (IUCN) which advises the Unesco world heritage committee said that the organisation was receiving “a lot of worrying information” about logging activity in Białowieża.

“The IUCN is planning a mission to Białowieża next month to assess the situation and the effect of the new logging plans on the World Heritage site. We would advise that, as a precautionary approach, logging should not be proceeding in the Białowieża forest until there has been an assessment of its implications for its world heritage status,” he said.