A video grab shows Pope Francis kissing the nun.

Pope Francis warned a nun not to bite him in a joking reference to his run-in with an overly zealous pilgrim last week, which saw him slap the woman's hand.

"I'll give you a kiss, but you must stay calm. Don't bite!" he told the enthusiastic nun, who had been shouting "Long live the pope!" as Francis greeted pilgrims before his weekly general audience.

The 83-year old Argentinian then bent to kiss her on the cheek, sparking cheers from fellow worshippers in the crowd.

It was the pope's first walkabout among the faithful since a pilgrim grasped his arm and tugged him towards her on New Year's Eve, prompting him to angrily swat her away in images that went viral on social media.

Francis apologised the next day, saying he too sometimes lost his patience.