The pope's open-air mass will be the grandest effort of his trip to rally the nation's Catholics, who account for 55 percent of the population, and follows a Saturday night event for Angolan youth that drew more than 30,000 people into a Luanda stadium.
A stampede when the gates of the stadium opened at midday killed two young people and injured 18, senior police official Paulo de Almeida told Portugal's Lusa news agency.
The two -- a male and a female whose ages were not clear -- died at the scene. Ten others were treated on the spot and eight taken to hospital, Lusa said.
"The Holy Father will speak about this tragedy during a Mass he is due to hold on Sunday," in Luanda, Vatican spokesman Federico Lombardi told AFP.
Angola is home to one of the oldest Catholic communities in sub-Saharan Africa -- the religion arrived with the Portuguese 500 years ago -- but now faces growing competitors for the faith of the nation.
Organised evangelical churches, traditional faiths and home-grown sects are all growing in popularity, even though some of the shadier sects have been implicated in child abuse scandals and even human sacrifice.
On Saturday, Benedict condemned the practice of witchcraft and urged Catholic clergy and laypeople to convert more people to the faith.
"So many of them are living in fear of spirits, of malign and threatening powers. In their bewilderment they end up even condemning street children and the elderly as alleged sorcerers," Benedict said.
"Today it is up to you, brothers and sisters, following in the footsteps of those heroic and holy heralds of God, to offer the risen Christ to your fellow citizens," he said Saturday.
The church remains one of the few strong national voices outside of government in Angola, running a radio station in Luanda known for broadcasting dissenting views.
Local church leaders hope the pope's visit will push Angola's government -- run by the formerly Marxist Popular Movement for the Liberation of Angola -- to allow Radio Ecclesia to broadcast nationwide.
In a speech at President Jose Eduardo dos Santos's residence late Friday, Benedict urged African leaders to allow greater press freedom, as he made a stern call for the continent to do more to fight poverty and corruption.
Dos Santos has ruled Angola for 30 years, and the country is ranked among the most corrupt in the world by Transparency International.
Benedict called on Africa to show "a determination born from the conversion of hearts to excise corruption once and for all".
"Armed with integrity, magnanimity and compassion, you can transform this continent, freeing your people from the scourges of greed, violence and unrest," he said.
Benedict has also sought to reinforce Catholic teachings on social issues, including condoms and abortion, but the Vatican on Saturday softened his remarks on abortion, saying the church did not oppose medical care for mothers that results in the unintentional death of the foetus.