An election commission official in Luanda said the People's Movement for the Liberation of Angola (MPLA) had won just over 64 per cent of the ballot.
The partial results from Wednesday's vote account for two-thirds of all polling stations, with the MPLA building an unassailable lead over its rivals.
The party, which has ruled since Angola's hard-fought independence from Portugal in 1975, had predicted an easy victory, but the outcome indicated a fall in its support since the previous election in 2012.
Lourenco, until recently defence minister, has vowed to boost foreign investment and said he wants to be recognised as a leader who brought an "economic miracle" to the southern African country.
He is expected to formally assume power next month.
The two main opposition parties, UNITA and Casa-CE, immediately alleged that the vote count was flawed.
"We have results different from those announced," UNITA representative Estevao Jose Kachiungu told reporters.
"It is impossible in the current Angola that the MPLA wins in all provinces with such a gap."
Opposition leaders earlier complained they had been deprived of media access and that voters in opposition strongholds were forced to cast their ballots at polling stations far from their homes.
UNITA took 24 percent of the votes and Casa-CE 8.5 percent, according to the partial results.
The two parties had hoped to tap into public anger over inflation that peaked at more than 40 percent last year, as well as low growth and high unemployment.
Despite being rich in oil and diamonds, Angola remains one of the poorest countries in the world and one of the most closed societies on the African continent.
"It will politically strengthen president-elect Joao Lourenco. Angola's economy is in crisis and he needed a strong mandate to deal with it."
Before the results were released, the MPLA's central committee spokesman Joao Martins declared in the local media that the party's victory was "unequivocal and virtually unavoidable".
Dos Santos's long reign saw the end of Angola's bloody civil war between 1975 and 2002 and a post-conflict investment boom as the country exploited its oil reserves.
"I am waiting for things to change, for more work, more schools, more hospitals and everything else," MPLA supporter Rosaria Almeida said as she cast her ballot on Wednesday.
The MPLA, which won 72 percent in the 2012 election, funded a recent rush of infrastructure projects, apparently to shore up support levels among Angola's 9.3 million registered voters.
Dos Santos has been dogged by reports of illness, with his regular visits to Spain for "private" reasons fuelling criticism that the state of his health was being hidden from ordinary Angolans.
At a weekend rally in front of thousands of party supporters, Dos Santos, a frail-looking 74, made a brief appearance to endorse Lourenco.
Amnesty International called for Angola's next leader to "guide the country out of the spiral of oppression" and castigated Dos Santos's "appalling human rights record".
Critics often accuse him of ruthlessly suppressing dissent and enriching his family and the ruling elite.
Dos Santos is to remain MPLA party chief, and new laws passed last month have limited the unfettered presidential power he enjoyed.
Disclaimer: No Business Standard Journalist was involved in creation of this content
You’ve reached your limit of {{free_limit}} free articles this month.
Subscribe now for unlimited access.
Already subscribed? Log in
Subscribe to read the full story →
Smart Quarterly
₹900
3 Months
₹300/Month
Smart Essential
₹2,700
1 Year
₹225/Month
Super Saver
₹3,900
2 Years
₹162/Month
Renews automatically, cancel anytime
Here’s what’s included in our digital subscription plans
Exclusive premium stories online
Over 30 premium stories daily, handpicked by our editors


Complimentary Access to The New York Times
News, Games, Cooking, Audio, Wirecutter & The Athletic
Business Standard Epaper
Digital replica of our daily newspaper — with options to read, save, and share


Curated Newsletters
Insights on markets, finance, politics, tech, and more delivered to your inbox
Market Analysis & Investment Insights
In-depth market analysis & insights with access to The Smart Investor


Archives
Repository of articles and publications dating back to 1997
Ad-free Reading
Uninterrupted reading experience with no advertisements


Seamless Access Across All Devices
Access Business Standard across devices — mobile, tablet, or PC, via web or app
