Hundreds of Romanians protested in several cities on Thursday against plans for shale gas exploration, known as fracking, voicing concerns over environmental pollution and health hazards.

"Exploiting shale gas threatens to contaminate ground water and I don't want us and our children to some day be forced to drink infested water," one of the protesters, Cristian Popescu, a 42-year-old public servant, told AFP.

Around 300 protesters gathered in Bucharest's University Square denounced the drilling technique, called hydraulic fracturing or 'fracking', which uses high pressure injections of water, sand and chemicals to crack open rock and release oil and gas trapped inside.

"This controversial method has been banned by countries such as France and Bulgaria," Georgeta Mihail, a 60-year-old German teacher said.

The protesters called on the centre-left government to revoke permits granted to several oil groups, including US giant Chevron, enabling them to start exploration drilling.

"Chevron, go home," and "Down with traitors", they chanted, in reference to Prime Minister Victor Ponta who earlier this year said he was favourable to fracking after having said he was against it while in opposition.

Nearly 1,000 people rallied in Barlad, an eastern Romanian city lying close to a 600,000 hectare concession granted to Chevron.

"We don't want to be the Guinea pigs of those who back shale gas exploitation," Vasile Laiu, a priest heading the local opposition to fracking told the protesters.

Several hundred people also staged a protest in Buzias, a resort famous for its mineral water lying in a western Romanian region where a Luxembourg-based company plans to start drilling.

The highly controversial fracking technique, invented in 2007, has unlocked immense gas and oil resources, changing the geopolitics of energy in what has become the gold rush of the 21st century.

A U.S. Energy Information Administration study said the joint reserves for Romania, Bulgaria and Hungary were around 538 billion cubic metres, among the biggest in eastern Europe.

If exploited, this could allow them to break free from their reliance on gas from Russia.