An employee prepares ballots in a polling station in Athens on May 18, 2014

Greece's radical leftist party Syriza, which opposes the government's austerity policies, was leading in the Athens area, exit polls of the first round of local elections showed on Sunday.

Syriza's candidates for the capital's mayor as well as regional governor in greater Athens are ahead in the race against the incumbent socialist office-holders, the televised polls showed.

The party's candidates have between 20 and 31 percent of the vote. A result of at least 50 percent is required for an outright win in the second round on May 25.

The pro-government mayor of the main port of Piraeus is also lagging behind a candidate openly backed by the city's favourite sports club, Olympiakos.

The local ballot is expected to gauge remaining support for the embattled government coalition after two years of unpopular austerity reforms in return for EU-IMF bailout loans.

Candidates put forward by the neo-Nazi party Golden Dawn look set to score double-digit results despite an ongoing criminal investigation against the party.

Golden Dawn's candidates for Athens mayor and regional governor are likely to receive between nine and 17 percent of the vote, the exit polls showed.

Syriza want to use these local elections -- and the European polls next week -- as a referendum against austerity and springboard for general elections, which could come as early as February next year.

Ten million voters were registered to elect 325 mayors and 13 regional governors across the country, with second rounds to be held on May 25 where necessary.