Leo was travelling on Friday to Douala, Cameroon's main port city, to celebrate mass and visit a hospital.
The Vatican predicted some 600,000 people would turn out for the liturgy, the biggest crowd Leo is expected to draw on his 11-day odyssey, the first to Africa by history's first American pope.
Later on Friday back in the capital Youande, Leo has an appointment with students, professors and administrators at the Catholic University of Central Africa.
Popes have often used such encounters, especially in the developing world, to rally young people to persevere in the face of poverty, corruption and other challenges.
Catholics represent about 30 per cent of Cameroon's 29 million people.
It is an overwhelmingly young country, where the median age is 18.
Leo has already offered words of encouragement to Cameroon's youth, including in his opening speech to President Paul Biya, at 93 the world's oldest leader.
In the speech, Leo demanded the "chains of corruption" in Cameroon be broken and said Cameroon's youth represent the future and hope of the country.
But with Biya in power since 1982, Cameroon perhaps represents the most dramatic example of the tension between Africa's youth and the continent's many aging leaders.
Despite being an oil-producing country experiencing modest economic growth, young people say the benefits have not trickled down beyond the elites.
"Of course, when unemployment and social exclusion persist, frustration can lead to violence," Leo warned in his opening address to Biya and government authorities earlier this week.
"Investing in the education, training, and entrepreneurship of young people is, therefore, a strategic choice for peace.
"It is the only way to curb the outflow of wonderful talent to other parts of the world."
Growing frustration over Biya's record and long-term rule intensified during last October's tense presidential election, in which Biya secured an eighth consecutive term.
When Cameroon's main opposition candidate, Issa Tchiroma Bakary, contested the result of the poll, deadly protests erupted throughout the country.
