Nursing mothers should be free to breastfeed in church "without fear", Pope Francis told women attending a ceremony in the Sistine Chapel on Sunday.

"The ceremony is a little long, someone's crying because he's hungry. That's the way it is," the Pope said during a baptism service, according to AFP.

"You mothers, go ahead and breastfeed, without fear. Just like the Virgin Mary nursed Jesus," he added.

The service was held to commemorate the baptism of Jesus, and the Pope himself baptised 15 boys and 13 girls on the day.

It is not the first time the Pontiff has spoken out on the issue of breastfeeding in public. In January 2015, he told nursing mothers, again in the Sistine Chapel, "You mothers give your children milk and even now, if they cry because they are hungry, breastfeed them, don't worry... Because they are the most important people here."

He also asked those gathered to remember those across the world who can't afford to "give food to their children".

In an interview with La Stampa the previous December, he recalled an encounter with a mother at a general audience whose baby was crying.

"I said to her: 'Madam, I think the child's hungry.' 'Yes, it's probably time...' she replied. 'Please give it something to eat!' I said. She was shy and didn't want to breastfeed in public, while the Pope was passing. I wish to say the same to humanity: give people something to eat!" Francis said.

"That woman had milk to give to her child; we have enough food in the world to feed everyone. If we work with humanitarian organisations and are able to agree all together not to waste food, sending it instead to those who need it, we could do so much to help solve the problem of hunger in the world. I would like to repeat to humanity what I said to that mother: give food to those who are hungry! May the hope and tenderness of the Christmas of the Lord shake off our indifference."