Mother Teresa has been proclaimed a saint by Pope Francis in front of 100,000 Catholics this morning.

Mother Teresa, the tiny nun who cared for the world's most unwanted and became an icon of the Catholic Church, was canonised at a ceremony in St Peter's Square.

Two supposedly miraculous cures have been attributed to Mother Teresa by the Vatican, paving the way for her sainthood.

At least 100,000 pilgrims and tourists were expected at the ticketed ceremony this morning, as well as dozens of heads of state.

Pope Francis, who yesterday decried the modern 'sin of indifference' to suffering, presided over the morning Mass.

'For the honour of the Blessed Trinity... we declare and define Blessed Teresa of Kolkata to be a Saint and we enroll her among the Saints, decreeing that she is to be venerated as such by the whole Church,' the pontiff said in Latin.

Applause erupted in St Peter's Square even before Francis finished pronouncing the rite of canonisation at the start of Mass, evidence of the admiration Mother Teresa enjoyed from Christians and non-Christians alike.

For the Pope, Mother Teresa put into action his ideal for the church to be a merciful 'field hospital' for the poorest of the poor, those suffering both material and spiritual poverty.

Yesterday he praised the care Mother Teresa had for the poor and the sick, while taking a swipe at world leaders for their 'sin of indifference' to suffering today.

'Tomorrow, we'll have the joy of seeing Mother Teresa proclaimed a saint,' he said. 'She deserves it!'

The pontiff decried those who 'turn the other way not to see the many forms of poverty that begs out for mercy'.