Ranks of Myanmar nuns in habits sang in Latin, backed by organ music as Francis delivered a homily urging compassion, opening his speech with 'minglabar', Burmese for hello.
"I can see that the Church here is alive," he said of a Catholic community numbering around 700,000 -- a tiny fraction of the country's 51 million population, most of whom are Buddhists.
Earlier Francis smiled and waved as he snaked through the estimated 150,000 faithful in his "popemobile", many of the worshippers holding Myanmar flags and wearing colourful clothes from the country's myriad ethnic groups.
"I never dreamed I would see him (the pope) in my lifetime," said Meo, an 81-year-old from the Akha minority in Shan state.
Like many others at the mass she is from one of Myanmar's conflict-riddled borderlands, and travelled far to reach the commercial capital for the landmark visit.
"This is the most Catholics I have ever seen," added Gregory Than Zaw, 40, an ethnic Karen, who made the five-hour bus journey to Yangon with 90 people from his village.
The pope is set to hold a meeting with Buddhist leaders later Wednesday, on a visit that has also been heavily political as well as religious.
Francis has held private talks with both civilian leader Aung San Suu Kyi and the powerful army chief Min Aung Hlaing.
'Respect for rights'
The pontiff arrived on Monday in a country on the defensive after outcry from the international community over the plight of its unwanted Rohingya Muslim population, who have been driven to Bangladesh in huge numbers.
The pope avoided mentioning the crisis -- or the Rohingya -- directly in a speech the country's capital on Tuesday, calling simply for "respect for rights and justice".
His caution so far on a four-day trip will bring relief to Myanmar's Catholic leaders who had urged the pontiff not to wade into the treacherous issue.
The Rohingya are denied citizenship, and even mention of their name is unacceptable to many among the majority-Buddhist population.
A military crackdown has forced more than 620,000 Rohingya over the last three months to flee their homes in northern Rakhine state to what is now the biggest refugee camp in the world in neighbouring Bangladesh.
The army has justified the campaign as a proportionate retaliation for attacks by hardline Rohingya militants in August.
But the UN and the US have labelled it ethnic cleansing and rights groups accuse the military of crimes against humanity, with refugees recounting consistent reports of murder, rape and arson.
On December 5 the UN's Human Rights Council will hold a special session to discuss the Rohingya crisis.
There have been Catholics in Myanmar for over 500 years and they generally enjoy good relations with the Buddhist majority.
In the last three years, the Vatican has canonised Myanmar's first saint and named its first cardinal before full diplomatic ties were established in May this year, which paved the way for the pontiff's visit.
"When we heard the sound of his words, we could tell they came from the heart... and that gives us peace," 47-year-old Yangon resident Ko Ko Lay told AFP, after the mass had finished.
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