Mother Teresa, the celebrated nun whose work with the poor of Kolkata made her an instantly recognisable global figure, will be proclaimed a saint on Sunday.

Pope Francis will preside over a solemn canonisation mass in the presence of 100,000 pilgrims and with a giant haloed portrait of Teresa smiling down from St Peter's Basilica.

The sainthood ceremony, for which the Vatican could easily have issued twice as many tickets, comes one day short of the 19th anniversary of Teresa's death, at 87, in the Indian city where she spent her adult life, first teaching, then tending to the dying poor.

It was in the latter role, at the head of her own still-active order, the Missionaries of Charity, that Teresa became one of the most famous women on the planet.

Born to Kosovar Albanian parents in Skopje -- then part of the Ottoman empire, now the capital of Macedonia -- she won the 1979 Nobel peace prize and was revered around the world as a beacon for the Christian values of self-sacrifice and charity.

She was simultaneously regarded with scorn by secular critics who accused her of being more concerned with evangelism than with improving the lot of the poor.

The debate over the nun's legacy has continued after her death with researchers uncovering financial irregularities in the running of her Order and evidence mounting of patient neglect, insalubrious conditions and questionable conversions of the vulnerable in her missions.

A picture of her as someone who was just as comfortable flying around in a private plane as clutching the hand of a dying patient has also emerged to counterbalance her saintly image.

- Miracles or medicine -

Sceptics will be absent from the Vatican Sunday however as Francis pays homage to a woman he sees as the embodiment of his vision of a "poor church for the poor".

"Tomorrow we will have the joy of seeing Mother Teresa proclaimed a saint," the Argentinian pontiff said on Saturday. "And how she deserves to be!"

"This witness to mercy in our time will join the vast array of men and women who, by their holiness of life, have made the love of Christ visible."

By historical standards, Teresa has been fast-tracked to sainthood, thanks largely to one of the few people to have achieved canonisation faster, John Paul II.

The Polish cleric was a personal friend of Teresa and as the pope at the time of her death, he was responsible for her being beatified in 2003.

Achieving sainthood requires the Vatican to approve accounts of two miracles occurring as a result of prayers for Teresa's intercession.

The first one, ratified in 2002, was of an Indian woman, Monica Besra, who says she recovered from ovarian cancer a year after Teresa's death -- something local health officials have put down to medical advances rather than the power of prayer.

In the second, approved last year, Brazilian Marcilio Haddad Andrino says his wife's prayers to Teresa led to brain tumours disappearing. Eight years later, Andrino and his wife Fernanda will be in the congregation on Sunday.

- Unique example -

Also among the crowd at St Peter's will be Teresa Burley, an Italy-based American teacher of children with learning difficulties who says the soon-to-be Saint Teresa inspired her vocation.

"I'm also named Teresa," she told AFP. "I remember growing up admiring the things she did for children and the poor.

"We need to remember we are here to help each other. We need to be here for those who can't help themselves. It's the same for refugees arriving here: we have to be there to help them transition into their new lives."

Many Indians have made the trip to Rome, among them Kiran Kakumanu, 40, who was blessed by Teresa when he was a baby and grew up to become a priest.

Abraham, an Indian expatriate in London, said Teresa's life had set a unique example to the world.

"She practised Christianity. The majority of Christians only spend their time talking about it."