A Hungarian opposition party says its private meetings in parliament were bugged, and politically sensitive material leaked from them, in order to undermine its election campaign.

Párbeszéd, a pro-EU and environmentalist party, has filed a criminal complaint with the police over the recordings, which are circulating on social media.

The recordings are of Gergely Karácsony, a candidate for mayor of Budapest standing for a bloc of left-liberal parties. In the tapes, he made politically sensitive comments about his allies and his chances at the election.

In a press conference on Sunday the party's leader Tímea Szabó alleged that the recordings had been taken and distorted to undermine Mr Karácsony's campaign.

“The case is Hungarian Watergate. This case is the biggest scandal in Hungary to date in the 21st century," she told the Hungarian press.

Ms Szabó says the recordings are cut from several different meetings, and that a party investigation had identified which gatherings and on what dates they had come from. The leader said that she had even recognised the voice of her own baby, which was at the meetings, in one of the clips.

She suggested that someone working for the parliament's administration might have eavesdropped on the meetings, but said it was up to investigators to find out who had conducted the alleged spying.

Hungarian politics is dominated by Viktor Orban's far-right Fidesz party, which is supported by a largely partisan pro-government media that marginalises opposition voices.

Hungary's Prime Minister Viktor Orban (REUTERS)

The country's government has been criticised by the European Commission and NGOs for breaches of the rule of law, which include allegations of restrictions on press freedom and the chipping away of judicial independence.

Earlier this year ruling party Fidesz was suspended from the main centre-right European People's Party group at EU level because of its approach to rule of law.