Eight political parties are running, but the real contest lies between the MPLA and its long-standing rival and ex-rebel movement the National Union for the Total Independence of Angola (UNITA).
Opinion polls suggest that support for the MPLA -- which won 61 percent of the vote in 2017 elections -- will dwindle, while the UNITA, which has entered an electoral pact with two other parties, will make gains.
An Afrobarometer survey in May showed the UNITA opposition coalition, led by Adalberto Costa Junior, increasing its share to 22%, from 13% in 2019.
That's still seven points behind the MPLA, but nearly half of voters were undecided. Many youths - under 25s make up 60% of the country - are voting for the first time.
But UNITA's inroads might not be enough to unseat Lourenco, 68, who succeeded veteran leader Jose Eduardo dos Santos five years ago.
"We have just exercised our right to vote. It's fast and simple. We advise all eligible citizens to do the same. In the end, we will all win, democracy wins and Angola wins," Lourenco told reporters at his polling station.
"The margins will be closer than ever before... but the advantages of incumbency mean MPLA is still odds on to pip Costa (Junior)," said Eric Humphery-Smith, an analyst at London-based Verisk Maplecroft.
Meanwhile, some voters say "It's been 20 years of peace and we are still poor," said Lindo, a 27-year-old electrician queueing up to vote in Nova Vida, a middle-class suburb of the capital Luanda.
"The people want change -- the government doesn't provide for people's basic needs," said Lindo, who gave only his first name.
"The process is proceeding in an orderly and peaceful manner. The general atmosphere is calm and there are no records of any disturbances that could jeopardize the process," a spokesperson for the National Electoral Commission told reporters on Wednesday morning.
Tweaked vote-counting rules may delay official results by days, analysts say, raising tensions which some fear may boil over into violence.
This article was compiled with information furnished by Reuters and Agence France-Presse.