Pope Francis on Thursday urged tens of thousands of young people in the Democratic Republic of Congo to work towards a better future and shun corruption in the deeply Catholic country, which is plagued by violence in its east.

The 86-year-old pontiff arrived at Martyrs' stadium in the capital Kinshasa on his popemobile, offering blessings to an ecstatic crowd, who roared and danced in the stands.

Young people started to flock to the 80,000-capacity stadium overnight. On Thursday, organisers put the size of the crowd at 65,000, on the third day of the Argentine's visit to Africa's biggest Catholic country.

About 60 per cent of the central African nation of roughly 100 million people are under the age of 20, according to UN figures. As well as conflict, young people face persistent unemployment.

Addressing the stadium, the pope urged the crowd to build a better future for the church and their country.

"You are part of a greater history, one that calls you to take an active role as a builder of communion, a champion of fraternity, an indomitable dreamer of a more united world," he said.

"Never give in to the persuasive but poisonous temptations of corruption," he said in Italian.

The pope also asked the crowd to chant "no to corruption" after him. Some of the youngsters chanted slogans hostile to Congolese President Felix Tshisekedi.

- 'Worldly comfort' -

Francis later on Thursday met Congolese Prime Minister Sama Lukonde at the Apostolic Nunciature in Kinshasa, the Holy See's diplomatic delegation.

He then met priests at the city's Notre Dame du Congo cathedral and warned them against the "temptation of worldly comfort".

About 40 per cent of the country's population is Catholic, according to official statistics, and the church retains huge influence despite secularism being enshrined in the constitution.

On Wednesday, the pope hosted a mass at Kinshasa's airport that organisers said drew about a million people, some of whom had camped out all night to get a spot.

He later met victims of conflict in the DRC's mineral-rich east, some of whom had suffered appalling violence.

His face grave, Francis called for mercy from God.

"May he convert the hearts of those who carry out brutal atrocities, which bring shame upon all humanity," he said.

He said the conflict was being driven by greed and called on combatants to lay down their arms.

"Listen to the cry of their blood," the pope said, alluding to a verse from the Book of Genesis.

Scores of armed groups roam eastern DRC, many of them a legacy of two wars at the end of the 20th century that sucked in countries from around the region.

- 'Economic colonialism' -

The DRC is replete with minerals, timber and fresh water, yet remains one of the poorest countries in the world where corruption is entrenched.

On Tuesday, the pope -- speaking before an audience of Congolese politicians and other dignitaries -- said the DRC had been hamstrung by a long history of exploitation.

"Political exploitation gave way to an economic colonialism that was equally enslaving," he said.

"As a result, this country, massively plundered, has not benefited adequately from its immense resources."

Many Congolese warmly welcomed the pope's message, and some hoped it would bring change.

On Friday morning, Francis will address Congolese bishops in Kinshasa before boarding a plane for South Sudan, where he will stay for three days.

The pontiff is expected to arrive at 3:00 pm local time (1300 GMT). He is due to greet the country's political leaders before making an address at the presidential palace.

Born in 2011 after gaining independence from Sudan, the nation has been battered by a civil conflict that left around 380,000 dead.

The visit to the two countries was initially scheduled for 2022 but had to be postponed because of the pope's problems with his knee -- an affliction that has made him dependent on a wheelchair.

It is his 40th foreign trip since he ascended to the papacy in 2013.