Venezuelans vote Sunday between continuity in President Nicolas Maduro or change in rival Edmundo Gonzalez Urrutia amid high tension following the incumbent’s threat of a “bloodbath” if he loses, which polls suggest is likely.

Concerns were further stoked when Caracas blocked several international observers at the last minute, including four ex-presidents who had their plane held up in Panama Friday.

Maduro, 61, is accused of locking up critics and harassing the opposition in a climate of rising authoritarianism.

He is seeking a third six-year term at the helm of the once wealthy petro-state that saw GDP drop 80 percent in a decade, pushing more than seven million of its 30 million citizens to emigrate.

Maduro lags far behind challenger Gonzalez Urrutia in voter intention, according to independent polls, but counts on a loyal electoral machinery, military leadership and state institutions in a system of well-established political patronage.