Hundreds of nuns, bishops and volunteers attended a Mass in Calcutta, where she founded the Missionaries of Charity to care for the poor and homeless.
School children, tourists and volunteers, some carrying bunches of flowers or candles, gathered at her grave.
Sister Mary Prema, the nun who now heads the order, says Mother Teresa's life and work "continue to be an inspiration for the young and the old, the rich and the poor, from all walks of life, religions and nations."
Special feasts to feed the poor, a festival of films on her life and work, the launch of a new train called the Mother Express, and interfaith prayer meetings are among the centennial events planned.
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