Poland on Wednesday said it had detected a leak in one of the Druzhba pipelines carrying oil from Russia to Europe, adding that it was probably caused by an accident, although the incident may still stoke concerns about the security of Europe's energy supplies.

The discovery of the leak in the main route carrying oil to Germany, which operator PERN said it found on Tuesday evening, comes as Europe faces a severe energy crisis in the aftermath of Moscow's "special military operation" in Ukraine.

"Here we can talk about accidental damage," Poland's top official in charge of energy infrastructure Mateusz Berger told Reuters by telephone. He said there were no grounds to believe the leak was caused by sabotage.

PERN said in a statement that at this point the exact causes of the leak were unknown. It was detected in a section of the pipe around 70 kilometres from the central Polish city of Plock.

A PERN spokesperson declined to give further details.

The Druzhba oil pipeline, whose name means "friendship" in Russian, is one of the world's largest, supplying Russian oil to much of central Europe including Germany, Poland, Belarus, Hungary, Slovakia, the Czech Republic and Austria.

"The main action (we are taking) is to pump out the liquid and locate the leak and stop it," fire brigade spokesman Karol Kierzkowski told Polish state broadcaster TVP Info.

"When the pressure decreases, the leak will stop and allow us to reach the leak," he said, adding that it was too early to establish the cause. He said there was no danger to local residents.

The second line of the pipeline, and other elements of PERN's infrastructure, were working as normal, PERN said.

"At this point, all PERN services (technical, operational, in-house fire brigade and environmental protection) are taking action in accordance with the algorithms provided for this type of situation," the operator said.

A spokesperson for the Czech pipeline operator MERO said it had not seen any change in flows to the Czech Republic.

Germany's Schwedt refinery, which supplies 90 percent of Berlin's fuel, its economy ministry and federal network regulator were not immediately available for comment.

The German government aims to eliminate imports of oil from Russia by the end of the year under European Union sanctions. But in the first seven months of the year, Russia was still its top supplier, accounting for just over 30 percent of oil imports.

The Schwedt refinery has been particularly dependent on Druzhba.

The German government has been in talks to secure oil from Kazakhstan to supply Schwedt, but even that oil would have to flow to Germany via the Druzhba pipeline.

The leak in the subsea Nord Stream 1 and 2 gas pipelines has been blamed on sabotage by both the West and Russia. It was not immediately clear how significant the leak in the Druzhba pipeline was.

(Cover: The receiver station of the Druzhba pipeline of petroleum between Hungary and Russia with a memorial plate of its construction at the Duna (Danube) Refinery of Hungarian MOL Company located near the town of Szazhalombatta, about 30 km south of Budapest, May 5, 2022. /CFP)