Many had already started setting up tents on the outskirts of the city on Friday, armed with posters of the Argentine pontiff.

Prospere Ralitason, a 70-year-old farm worker, arrived with some 5,000 fellow pilgrims from the central eastern town of Ambatondrazaka, 200 kilometres (125 miles) away.

"We are tired, but it's worth making all these sacrifices to see the pope with our own eyes and receive his blessing," he told AFP.

The mass at the Soamandrakiza stadium was due to begin at 10:00 am (0700 GMT).

The last pope to visit Madagascar was John Paul II 30 years ago.

In June, 16 people were killed and dozens hurt in a stampede outside a sports stadium in Antananarivo during a free concert.

Crowds gathered on Saturday to welcome the pope as he made his way in his popemobile to Soamandrakizay.

Thousands of young people -- mainly scouts -- gathered for a vigil there, waiting hours in the heat for Francis to arrive.

"I am here to ask for the pope's blessing to face the harsh realities of life, insecurity, poverty and corruption," said 17-year old student Njara Raherimana, who travelled hundreds of kilometres for the event.

"All this gives me hope for change in my country," echoed fellow student, Antony Christian Tovonalintsoa, who lives on the outskirts of the capital.

During the vigil, Pope Francis lauded the "joy and enthusiasm" of the singing crowd.

He encouraged the youth not to fall into "bitterness" or to lose hope, even when they lacked the "necessary minimum" to get by and when "educational opportunities were insufficient".

Earlier on Saturday, Francis also made an impassioned plea to Madagascans to protect the Indian Ocean's unique environment from "excessive deforestation".

Weeks after a spike in fires in the Amazon, the Argentine pontiff told his hosts they should "create jobs and money-making activities which respect the environment and help people escape poverty".

Madagascar -- famed for its immense diversity of flora and fauna -- is home to 25 million people, the vast majority of whom live in poverty on an income of less than two dollars a day.

More than half of its young people are out of work, even if many boast good qualifications.

Francis visited Mozambique earlier in the week. He is also due to travel to the island of Mauritius, which like Madagascar is situated off the eastern coast of Africa.