President Joao Lourenco and his main opposition rival Adalberto Costa Junior hope to win over the youthful and largely poor electorate in a race that could also affect pro-Russia ties.
Angolans have started voting in a tight race in which the main opposition coalition has its best-ever chance of victory, as millions of youth left out of its oil-fuelled booms are expected to express frustration with nearly five decades of the People's Movement for the Liberation of Angola (MPLA) rule.
The ruling party remains the favourite in Wednesday's election, though the margin is narrow enough for a surprise victory for the National Union for the Total Independence of Angola (UNITA), which could shift relations with global superpowers — with possibly less friendly ties with Russia.
Since independence from Portugal in 1975, Angola has been run by the formerly Marxist MPLA, led since 2017 by President Joao Lourenco.
But an Afrobarometer survey in May showed UNITA's opposition coalition, led by Adalberto Costa Junior, increasing its share to 22 percent, from 13 percent in 2019.
That's still seven points behind the MPLA, but nearly half of the voters were undecided. Many youths – under 25s make up 60 percent of the country – are voting for the first time.
In a tense run-up to the vote for both president and parliament, UNITA has urged voters to stay near polling stations after voting to reduce the risk of fraud.
Tweaked vote-counting rules may delay official results by days, analysts say, raising tensions – which some fear may boil over into violence.
A UNITA victory could weaken decades of close ties with Moscow, for whom the MPLA was a cold war proxy during Angola's 27-year civil war ending in 2002, while UNITA was US-backed.
UNITA condemned "the invasion of Ukraine by Russia," Costa Junior said on Twitter. He also travelled to Brussels and Washington to build ties with Western partners before the elections.
Russia's ambassador to Angola, Vladimir Tararov, was quoted in the Angolan press in March as praising the country for its neutrality while lambasting UNITA for wanting to show it "stands with the West, the so-called civilised countries".
Lourenco has also opened up to the West since his election in 2017, but in March it abstained from supporting a United Nations resolution which condemned Russia's assault on Ukraine.
"It is highly possible that a UNITA win would mean a distancing of Angola from Russia," Charles Ray, head of the Africa Programme at the Foreign Policy Research Institute, told the Reuters news agency, but only if it can consolidate power over a pro-Russian military first.
Lourenco has tried to improve relations with Washington, and just before the elections applied to join a trade agreement with the European Union and southern African states, which has been in force since 2016. Talks start in months.
Angola, a former colony of Portugal, is a major producer of oil and diamonds yet years of civil war and corruption have left many Angolans in poverty.
Angola's economy is battling an economic recession and inflation which has caused the cost of living to soar in urban areas. A severe drought has parched Angola's southern provinces, affecting more than two million people.