Poland on Tuesday began logging in the ancient Bialowieza 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 told reporters the goal was "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.

But 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 to its tallest trees.

"We're calling on the European Commission to intervene before the Polish government allows for the irreversible destruction of the Bialowieza forest," Greenpeace Poland activist Katarzyna Jagiello said in a statement.

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," Jagiello told AFP.

Greenpeace said its patrols had come across the first signs of logging between the eastern town of Hajnowka on the border with Belarus and the village of Bialowieza to the north.

The Bialowieza 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 (6.4 million 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 told AFP at the time that the Commission "is concerned" about the project.

- Nature 'to fend for itself' -

Bialowieza, which was designated a UNESCO World Heritage site in 1979, covers about 150,000 hectares (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 (160 feet) 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".

Environment Minister Jan 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.

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 Bialowieza between June 4 and 8 to assess the situation.