Bulgaria`s centre-right Prime Minister Boyko Borisov stepped down Sunday after his presidential nominee suffered a crushing defeat at the hands of a Moscow-friendly general backed by the Socialist opposition.
Observers say the surprise win could tilt ex-communist Bulgaria, which has long walked a tightrope between Moscow and Brussels, towards Russia`s orbit -- a trend seen across eastern and central Europe amid rising euroscepticism.
Nearby Moldova also looked set to elect a pro-Russian president on Sunday.
"I will hand in my resignation tomorrow or the day after.... The results clearly show that the ruling coalition no longer holds the majority," the premier told reporters on Sunday evening.
The announcement is likely to trigger early elections by next spring and risks plunging Bulgaria into renewed political turmoil just two years after Borisov and his GERB party took office for the second time.
It came shortly after projections showed that ex-airforce chief and political novice Rumen Radev had swept close to 60 percent of ballots. Borisov`s nominee ex-parliament speaker Tsetska Tsacheva obtained just over 35 percent.
"It`s a victory for all Bulgarian people. Democracy has beaten apathy and fear today," Radev told public broadcaster BNT on Sunday evening.
The straight-laced Tsacheva meanwhile failed to sway disgruntled voters seeking to punish the government over its perceived failure to tackle rampant corruption and poverty in the European Union`s poorest member state.
"I voted against Borisov because I don`t think that he`s honest and he hasn`t really done anything to improve our lives," said 52-year-old Zora Kardachka, a dry cleaner.
Gallup director Parvan Simeonov said the outcome was a "clear protest vote".
Despite promised reforms, graft and poverty remain rife in the EU`s poorest member state, while public anger has also grown over thousands of migrants currently stranded in Bulgaria.
"Bulgaria needs a new face, someone who defends national interests instead of always saying `Yes` to the European Union and the United States," businessman Assen Dragov, 39, told AFP after casting his vote in Sofia.
The Bulgarian president`s role is largely ceremonial but the incumbent is nonetheless a respected figure and commander-in-chief of the armed forces.National security and preventing a new migrant influx featured highly during Radev`s campaign, which saw the general gaining confidence and projecting himself as a fierce critic of the conservative status-quo.
His clear support for the lifting of EU sanctions on Russia over Ukraine and ambivalent statements about the EU and NATO have prompted analysts to speculate that he could pursue closer ties with Moscow.
"General Radev`s victory represents the unfolding of a pro-Russian scenario in Bulgaria so that the country supports Russian interests in the EU and NATO," political expert Antoniy Galabov told AFP.
Russia and Bulgaria have deep historical and cultural ties, and Bulgaria is heavily reliant on Russian gas.
Outgoing President Rosen Plevneliev, a strong critic of Moscow, warned Sunday that Russia was trying to "destabilise Europe" by financing anti-EU ultra-nationalists including in Bulgaria.
"The (climate) is more dangerous now than during the Cold War," he told Austrian media.
"Those who seek to destabilise Europe, have the best chances of doing so in the Balkans. It`s always been this way: this is where WWI was ignited."