Mother Teresa is officially a saint of the Roman Catholic Church, 19 years after her death.

The ceremony to canonise the Nobel peace prize laureate, who is recognised globally for her work with poor people in the slums of Kolkata in India, drew 100,000 people from around the world to St Peter’s Square in Vatican City.

“For the honour of the Blessed Trinity … we declare and define Blessed Teresa of Kolkata to be a saint and we enrol her among the saints, decreeing that she is to be venerated as such by the whole Church,” Pope Francis said in Latin.

Her path to canonisation was sealed after the Vatican last year recognised the second of two required miracles, following her death.

Mother Teresa accompanied by children at her mission in Calcutta in 2005. Photo: Getty

A guide to becoming a saint

Mother Teresa’s canonisation is even more significant when one considers the strict rules of Catholic sainthood.

The process of becoming a saint usually does not even begin until at least five years after the person’s death – to allow for emotions to settle and to promote an objective evaluation.

For some it’s considerably more than five years; St Bede died in 735 and was canonised in 1899.

Next, the person’s virtue and holiness are investigated before they can be declared a “servant of God”.

Then their work must be deemed to be of “heroic value”, or, that others have prayed using them as an example.

Finally, it’s time for the miracles. To be proclaimed a saint, the church must verify two miracles attributed to people praying through the person in question.

In 1997, Monica Besra, a tribal woman of West Bengal is said to have been cured of a tumour after nuns prayed to Mother Teresa and placed a pendant around her belly.

Queen Elizabeth presents the Order of Merit to Mother Teresa in 1982. Photo: Getty

Besra awoke the next morning to find her tumour gone, although numerous doctors and even her husband have argued it was the result of medicine.

Similarly in 2008, Brazilian man Marcilio Haddad Andrino recovered from multiple abscesses in his brain.

Pilgrims pack St Peter’s Basilica

Her legacy complements Pope Francis’s vision of a humble church that strives to serve the poor, and the festivities are a highlight of his Holy Year of Mercy, which runs until November 8.

St Peter’s Basilica was decked out with a canvas of the late nun in her trademark blue-hemmed white robes.

Crowds flock to the Vatican for Mother Teresa’s canonisation. Photo: AP

In Kolkata, where Mother Teresa was laid to rest, singing nuns and followers clutching flowers flocked to her tomb to celebrate her proclamation.

People started gathering from early morning at Mother House in Kolkata for a special mass for the “Saint of the Gutters” ahead of the ceremony.

The canonisation was also celebrated in Skopje, the capital of modern Macedonia where Mother Teresa was born of Albanian parents in 1910 and became a nun aged 16.

Sunday’s ceremony comes one day short of the 19th anniversary of Teresa’s death, at 87, in Kolkata.

The basilica was decked out with familiar images of Mother Teresa. Photo: ABC

-with agencies