Hundreds of thousands of pilgrims are attending a Mass celebrated by Pope Francis in Uganda.

Pope Francis is speaking at a Catholic shrine dedicated to Christians martyred for their faith in the 19th Century, on the second stage of his three-country trip to Africa.

The Mass marks the 50th anniversary of the martyrs’ canonization.

There were huge cheers as Pope Francis began the open-air ceremony at Namugongo, near Kampala.

It was there where many of the 45 Anglican and Catholic martyrs were burned alive.

The martyr’s execution was ordered by a king worried about the spread of Christianity.

Thousands of pilgrims braved rain to spend the night holding a vigil near the martyrs’ shrines and there were long lines of pilgrims still trying to access the shrine as Pope Francis began to address the crowds on Saturday morning.

Uganda is a deeply religious country, with over 14.1 million Catholics – and even adherents of other faiths will be paying close attention to the Pope’s words, say correspondents.

Pope Francis arrives in Uganda during the third week of a presidential campaign being fought by the country’s ruler for the past 29 years, President Yoweri Museveni.

Francis is the third Pope to visit Uganda, and he is likely to continue to preach his message of mercy and care for the poor, and to speak out against corruption – a message that was welcomed by people in Kenya.

The pontiff may also talk of the need for reconciliation amongst different tribes and, perhaps, pray for a peaceful vote here in February 2016.

However, there were critical references to the Pope’s visit on Twitter – with some wondering “how many people have HIV today because contraception isn’t allowed?” while others accused him of ignoring extreme anti-gay attitudes in Uganda.

Pope Francis will travel to the Central African Republic (CAR), which has been hit by serious violence between Christian and Muslim militias in recent years, on November 29.