Pope Benedict XVI proclaimed four new saints at a canonization ceremony in Saint Peter's Square on Sunday.

They include a French-born American nun, a Mexican bishop and two Italian founders of religious orders.

"We register them in the roll call of the saints and we establish that in all the Church they will be devotedly honoured among the saints," the pontiff said as he read the canonization ritual in Latin.

Many Mexicans turned out in Saint Peter's Square for the ceremony to honour one of their own, Bishop Rafael Guizar Valencia, who risked his life to assist the wounded during the Mexican revolution.

The Pope said the bishop of Veracruz-Xalapa, who was born into a wealthy family, was a hero to the poor.

With the start of the Mexican revolution in 1910, persecution of the Catholic Church became severe, and Guizar became a target, the Christian Newswire said on its website. Guizar, it said, went underground, disguised as a junk dealer, to continue his work as a priest.

Americans were also present to celebrate Mother Thedore Guerin, who endured harsh conditions in what was American frontier land. At the start of the 19th century she pursued her dream of establishing Catholic education for pioneers.

Pope Benedict said she overcame many challenges, and by the time she died, nuns of her order were running schools and orphanages throughout the state of Indiana.

Two other new saints include Filippo Smaldone, an Italian priest who worked with the deaf, and Rosa Venerini, an Italian nun who pushed for education for girls.