Thousands of devotees thronged to the headquarters of the Missionaries of Charity in the Indian city of Kolkata on Wednesday to offer prayers for Mother Teresa on the tenth anniversary of her death.

The doors of Mother House, where the ethnic Albanian nun lived and died, were thrown open at dawn and hundreds of slum dwellers from the city walked in.

Holding candles, they knelt before Mother Teresa's tomb in one of the sprawling halls of the building and prayed as nuns clad in traditional white saris with blue borders joined them.

"She was a great social worker with a strong heart to help all the poor. She is God's secretary," said Pushpa, a middle-aged woman who came all the way from the southern state of Kerala to pray for her cancer-stricken mother.

A few dozen people from a rationalist society shouted slogans outside, saying Mother Teresa should not be portrayed as a saint -- reflecting criticism in some Indian circles over her opposition to birth control and abortion.

Kolkata -- previously known as Calcutta -- was also painted as a pit of misery and suffering, critics argued, ignoring its long history of intellectual and artistic creativity.

Mother Teresa made Kolkata her home and opened several homes, including one for those who were old and dying and the other for destitute children.

Archbishop of Kolkata, Lucas Sircar, led a special mass where rich and poor sat together in prayer.

As people sang hymns, Sister Nirmala, the superior general of the order, held her palms together, occasionally waved at followers.

She succeeded the ailing Mother Teresa six months before she died, aged 87, on September 5, 1997.

"I am feeling deep joy and gratitude remembering Mother Teresa's presence today among us," she said as she placed a candle on the 1979 Nobel Peace Prize winner's tomb.

The doors of Mother House remained open throughout the day and hundreds of people walked in with palms pressed together, some carrying flowers.

"Mother helped me get a job and survive when there was nothing to look forward to in life," said Harihar Sahu, a blind man. "I hope she is made a saint soon."

Letters written by Mother Teresa to her colleagues and superiors over 66 years reveal she sometimes doubted God and tormented about her faith.

The collection of letters complied by an advocate for her sainthood was published on Tuesday under the title "Mother Teresa: Come Be My Light."

They cover a range of subjects dear to the nun, but it is those which portray her as at times deeply tormented about her faith that have grabbed attention.

There had been speculation the publication of the letters would hurt the procedure to make her a saint, but this weekend Pope Benedict said in a speech that Mother Teresa's torment over God's silence was not unusual.

"It is a day of remembering Mother Teresa for relentlessly working for our sick children day and night," said Seema Mondol, 60, tears rolling down her cheeks.