Pope Benedict XVI has celebrated an open-air mass for tens of thousands of people in the city of Santiago on the first day of his visit to Cuba.

The service in Santiago's Revolution Square was attended by President Raul Castro, who also welcomed the Pope when he flew in from Mexico.

Pope Benedict said he has come as a pilgrim of charity and would pray for peace, liberty and reconciliation.

He also expressed sympathy with the "just aspirations" of all Cuban people.

It is the first papal visit to the island for 14 years.

"I appeal to you to reinvigorate your faith ... and armed with peace, forgiveness and understanding, that you may strive to build a renewed and open society, a better society, one more worthy of humanity," the pontiff told the flag-waving throng in Santiago, massed under soaring white metal church arches.

The 84-year-old was helped up to his seat and smiled as the crowd sang and chanted to welcome him.

The crowd of an estimated 200,000 Catholics sang hymns, some joining their arms held high. Others folded their hands in prayer, listening intently to the pope's words. One worshipper waved a banner reading "It is good to trust the Lord."

The pontiff is working to try to expand the flock in Cuba, which was officially Atheist until the early 1990s.

"I carry in my heart the just aspirations and legitimate desires of all Cubans, wherever they may be, their sufferings and their joys, their concerns and their noblest desires," the pope said earlier in southeastern Santiago.

"I am convinced that Cuba, at this moment of particular importance in its history, is already looking to the future, and thus is striving to renew and broaden its horizons."

Marxism "no longer corresponds to reality," Pope Benedict said last week as he set off on his first trip to Spanish-speaking nations in Latin America, calling for "new models" in Cuba.

Cuba's leadership however says democracy already exists, and rejects the idea of a western multiparty system.

Before the mass, Benedict rolled in his white Popemobile down the streets of Santiago, as crowds of enthusiastic Cubans waved yellow and white Vatican and Cuban blue, white and red flags to greet him.

"Cuba has good relations with all religious institutions in our country," Raul Castro said as he welcomed the pope.

Authorities, meanwhile, have rounded up at least 150 dissidents in the past few days to thwart any possible demonstrations during the two-city papal visit, the head of an opposition group told AFP in Havana.