Arriving in the Cameroonian capital Yaounde, the pope said he was bringing the "Christian message of hope."
"In the face of suffering or violence, poverty or hunger, corruption or abuse of power, a Christian can never remain silent," he said after being greeted on the tarmac by Cameroon President Paul Biya.
"Even amid the greatest suffering, the Christian message always brings hope," the pope said.
In his welcoming remarks, Biya told the pope: "Africans and Cameroonians in particular ... note your unwavering interest in those who suffer from war, disease and oppression."
He added: "This solidarity is also an encouragement for them not to cede to pessimism on Africa and to continue their efforts to build a more just and united society."
Thousands of people, including entire families, groups of children in their school uniforms, clergy and percussion bands, lined the route from the airport to the papal nuncio's residence where the pope was to be lodged.
Benedict, who left behind controversy at the Vatican over his lifting of the excommunication of a Holocaust-denying bishop, also denied feeling alone over the affair.
"In truth, this myth about solitude makes me laugh," the pope said during the flight, dismissing reports in the Italian media that the controversy had left him isolated. "I am surrounded by friends. Solitude does not exist."
The pope, who will turn 82 on April 16, last month said he wanted 2009 to be the "Year of Africa," which will also include a conference of African bishops in Rome in September and an African synod at the Vatican in October.
The stop in Yaounde, where Benedict will stay until Friday, will include a meeting with the representatives of 52 African states preparing the October synod.
The capital -- where Benedict is to celebrate an open-air mass on Thursday -- has been spruced up, with public buildings repainted, roads repaired and trees and shrubs planted and trimmed.
Vatican and Cameroonian flags bearing photos of Benedict and Biya flutter throughout the city, particularly around the teeming John F. Kennedy avenue.
However, in a country of nearly 19 million people where development has been hampered by one of the highest levels of corruption in the world, many ordinary people are struggling to show enthusiasm.
"Pope Benedict is offering us his first visit to Africa. We are happy. However, no one is going crazy with delight," Catholic sociologist Pierre Titi Nwel told AFP.
In Angola, which is still recovering from 27 years of civil war, Benedict will meet with diplomats posted in Luanda and urge the international community not to abandon Africa.
Sub-Saharan Africa is more heavily affected by AIDS than any other region of the world. Nearly two-thirds of all adults and children with HIV live in the region, according to a 2006 report by UNAIDS.
AIDS prevention is a subject that often puts the Vatican at odds with international health organisations, since the Roman Catholic Church advocates abstinence as the only effective way of preventing the spread of AIDS and opposes campaigns for the use of condoms.
In June 2005, the pope told southern African bishops visiting the Vatican: "The traditional teaching of the Church has proven to be the only failsafe way to prevent the spread of HIV/AIDS."
Vatican watchers said they had never heard Benedict use the word "condom" before Tuesday.
While it is his first trip to Africa as pope, Benedict has travelled to the continent once before, as Cardinal Joseph Ratzinger in 1987 when he visited the Democratic Republic of Congo (then Zaire).
Image from BBC News.