Hungary's opposition Tisza party leads ruling Fidesz of Prime Minister Viktor Orban two days before parliamentary elections scheduled for Sunday, according to the latest polls.

Orban faces the biggest challenge of his 16-year rule, but the large number of undecided voters means the election outcome remains uncertain.

Tisza, led by former government insider Peter Magyar, enjoys support from 52 percent among decided voters, while Fidesz is backed by 39 percent.

When all voters are considered, 38 percent support Tisza and 29 percent Fidesz. About 25 percent said they have not yet decided.

The Hungarian elections are being closely watched by the EU and neighboring countries, given Orban's controversial foreign policy and close ties with Moscow and Beijing.