Pope Francis has started his 7-hour journey to Kenya where he is expected to arrive at 5pm.
He is aboard an Alitalia plane AZ 4000.
Other Vatican officials and a number of international journalists accredited to cover Pope Francis for his five-day visit of Kenya, Uganda and Central African Republic are on the same flight.
Pope Francis flew out of Rome on Wednesday, bound for Kenya on the first leg of a landmark trip to Africa that is fraught with security risks.
The 78-year-old pontiff, the third pope to visit the continent, is also scheduled to visit Uganda and the troubled Central African Republic (CAR) on a six-day trip.
The final leg of the tour, in the CAR, could yet be curtailed or cancelled depending on security conditions in a country that has been wracked by sectarian conflict in recent years.
A densely packed schedule will see the Pope visit, amongst others, a shanty-town in Kenya, a major Catholic shrine to Christian martyrs in Uganda and both a mosque and a refugee camp in the CAR.
He is due to make a series of speeches on various issues including a major one on the environment ahead of the Paris climate change summit.