Updated

Bulgarians are voting in a referendum on whether a new nuclear power plant should be built in the European Union's poorest member country, a choice also seen as a barometer of the country's relationship with Russia.

Sunday's vote was called by the opposition Socialist party in an effort to force the government to reverse its decision to scrap a deal with Russia on the construction of a second nuclear plant.

Bulgaria's first referendum since the fall of communism in 1989 has polarized opinion along party lines. It has been seen as a test ahead of general elections in July, but also as a chance to loosen Moscow's energy grip.

The latest polls estimate a low turnout, which could make the referendum invalid. At least 60 percent of the electorate must take part.