Thousands of Romanians protested on Monday against plans by the US company Chevron to explore for shale gas in eastern Romania.

"I have three children and I want them to grow up within a safe environment with clean water. Exploring for shale gas threatens to contaminate ground water," Alina Secrieru, a 39-year old nurse from the Barlad region told AFP.

"No fracking", "Chevron go home", "We say no to shale gas", read some of the banners carried by protesters who came from Barlad and surrounding villages.

Chevron obtained a vast concession in this poor and rural area of Romania to prospect for shale gas.

"This area survives on agriculture. If our water gets contaminated by the extraction of shale gas, agriculture will die and this area as well," said Constantin, a water specialist who was among the protesters.

He refused to give his last name out of fear of losing his job as most of the local politicians are now defending shale gas drilling.

Chevron has said in the past that all its activities "have, and will continue to be conducted in compliance with Romanian laws, EU requirements and stringent industry standards."

Shale gas drilling has fuelled controversy around the world.

The technique to extract the gas, hydraulic fraction or fracking, has been banned in countries such as France and Bulgaria but is widely used in some US states.

Fracking is a process whereby liquid products, including water and chemicals, are pumped deep into oil or gas-bearing rock to cause fractures and release the hydrocarbons.

Environmentalists say the method poses serious threats that include contaminating ground water and triggering earthquakes.

Romania together with Britain, Hungary, Poland and Spain strongly pleaded for developing shale energy during the last European council on energy.

Protesters lashed at centre-left Prime Minister Victor Ponta, accusing him of flip-flopping on his position against shale gas.

Ponta, in power since May 2012, had slammed the previous government's decision to grant Chevron and other oil groups concessions to prospect for shale gas.

His government last year adopted a moratorium on drilling, putting Chevron's operations on hold.

But since the moratorium expired in December, Ponta said he was in favour of exploration.

"Politicians have let us down but we want to remind them that the people in this area are against the exploration of shale gas. People here care about their environment" said Lulu Finaru, a notary who helped organise the protest.

A US Energy Information Administration study said the joint reserves for Romania, Bulgaria and Hungary were around 538 billion cubic metres (19 trillion cubic feet), among the biggest in eastern Europe.