Pope Francis steps onto African soil for the first time on Wednesday to address the continent's fast-growing Catholic congregation during a trip that will test his ability to bridge faultlines between Christians and Muslims.

The Nov. 25-30 tour starts in Kenya and Uganda, which have both seen Islamist militant attacks, before he travels to the Central African Republic, a nation torn by Muslim-Christian strife.

He is due to arrive in Nairobi at about 5 p.m. (1400 GMT).

"We are living at a time when religious believers, and persons of goodwill everywhere are called to foster mutual understanding and respect, and to support each other as members of our one human family," the pope said in a pre-trip message.

Millions of Christians - Catholics and others - are expected to turn out in welcome and for public celebrations of Mass, presenting a challenge for national security forces to keep the pontiff safe and control the huge crowds.

Africa's Catholic church is growing fast with an estimated 200 million adherents in 2012, a figure expected to reach half a billion in 2050. In Kenya, about 30 percent of the 45 million population are baptised Catholics, including President Uhuru Kenyatta.

"We are ready to receive him," Kenya's inspector general of police, Joseph Boinnet, told reporters. "Security arrangements have been put in place, right from arrival."

He did not say how many police would be deployed in the capital for the visit, which includes Mass at the University of Nairobi on Thursday, now declared a national holiday. Kenyan media has said at least 10,000 officers would be involved.

Kenya has been targeted by a spate of attacks by Somalia's Islamist group al Shabaab in the past two years that have killed hundreds of people. In 2013, an assault by al Shabaab gunmen on a Nairobi shopping mall killed 67 people.

He will also seek to heal ethnic rifts that have long plagued Kenya.

"Pope Francis' visit to Kenya will be focused on inclusivity and reconciliation in relation to ethnic and religious tolerance, peace and stability," Kenyan presidential spokesman Manoah Esipisu said.

The pope visits the Nairobi headquarters of the United Nations on Thursday and is expected to address climate issues.

In Uganda, where police said they would deploy 12,000 officers for the visit, the pope holds Mass on Saturday and then addresses young people on a continent that has a big youth belt.

Potentially the most hazardous stop of his trip is the third leg to the Central African Republic. Dozens of people have been killed there since September in violence between Muslim Seleka rebels and Christian anti-balaka militias.

His schedule in Bangui, the capital, includes a visit to a mosque in one of the most dangerous districts. French officials have hinted heavily that the Vatican should consider scrapping the Bangui leg of his trip or at least scaling it back.