Around 4,000 miners demonstrated in Athens Thursday to protest job cuts they fear will result from the hard-left government's opposition to continued exploitation of their gold mine in northern Greece.

Scores of buses transported miners from the Halkidiki region of Greece -- about 600 kilometres (370 miles) north of Athens -- to protest the Syriza-led government's decision last month to review the concession granted to the mine's Canadian operator, Eldorado Gold.

Though the mine represents one of the biggest foreign investments projects in Greece today, the government opposes further operation of the mine amid environmental and legal questions surrounding the concession.

The march represented one of the biggest labour protests since Syriza took power in January on promises of throwing off austerity and using public spending to spark economic growth.

The mine is located in a wooded area near the Mount Athos tourist destination. It has long been the source of repeated clashes between police and environmentalists backed by local residents, who claim the mine poses an ecological threat.

Opponents also denounce the financial terms of the concession granted by previous governments to Eldorado Gold -- objections the Syriza cabinet shares as it reviews the contract.

But the thousands of miners who descended on Athens Thursday to march by government ministries and parliament warned that putting the mine's future into question will lead to mass job cuts.

They noted that in a nation suffering 25.7 percent unemployment -- the highest level in the European Union -- Greece can scarcely risk provoking new job losses by meddling with the mine's operation.