Thousands marched Sunday across Romania to protest against a Canadian company's plans to open a gold mine seen as a threat to the environment, and called for the government's resignation.

In what has become one of the longest-running protests in post-communist Romania, an estimated 4,000 people demonstrated in the capital Bucharest to demand the mine project in Rosia Montana be dropped.

The protestors chanted slogans calling for the resignation of the centre-left government that adopted a draft law clearing the way for the open-cast mine planned by Canada's Gabriel Resources in the heart of Transylvania.

"We thought we were too small to change anything but these demonstrations have made us understand that we can change everything," one demonstrator, Alexandra Barradel, said.

"What is important now is to remain united to save Rosia Montana and Romania," she said.

The scope of the protest has grown over the past six weeks to reach unprecedented levels. Another 3,500 people took to the streets of the northwestern city of Cluj and another 600 demonstrated in Timisoara.

The Canadian company, which owns 80 percent of the Rosia Montana Gold Corporation, acquired a mining licence in 1999 but has been waiting ever since for a crucial permit from the environment ministry.

Gabriel Resources hopes to extract 300 tonnes of gold with mining techniques requiring the use of thousands of tonnes of cyanide.

It promises 900 jobs during the 16-year extraction period, as well as economic benefits.

But academics and environmentalists say the mine is an ecological time bomb and threatens the area's Roman mining galleries.

Prime Minister Victor Ponta had opposed the project when he was still a member of the opposition but he now faces Romania's largest protest movement in two decades for backing it.

The bill clearing the way for the mine has yet to be approved by parliament.

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