PHOTOS:Pope Francis loses his cool after being almost knocked over in Mexico

Calm, smiling and obliging, "serene" is among the adjectives most frequently deployed when describing Pope Francis.

It seems, however, that even the pontiff has his limits.

Francis, who is on a five-day trip to Mexico, was greeting fans at a stadium in the western city of Morella on Tuesday when he finally lost his cool with some overzealous well-wishers.

Following a colourful encounter with young dancers and singers, the pope went over to greet the faithful, at which point two arms reached out to grab him.

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The person, who is not seen in the video footage, did not let go, even after the pope lost his balance and fell onto a child in a wheelchair.

After aides and security men stopped the pope from falling to the ground, a flash of anger crossed his face as he stood upright.

Staring at the person, he raised his voice and said twice in Spanish: "Don't be selfish!"

Francis then took a couple of steps back as appeals came over the public address system asking the crowd not to clump together.

The Argentinian Pope has tried to get closer to the public, opting to use open-top cars instead a bullet-proof Popemobile used by his predecessors – a measure introduced after the attempted assassination of John Paul II in St Peter's Square in 1981.

"It's true that anything could happen, but let's face it, at my age I don't have much to lose," he said two years ago.

Francis wraps up his trip to Mexico on Wednesday with some of his most anticipated events: a visit in a Ciudad Juarez prison just days after a riot in another lockup killed 49 inmates and a stop at the Texas border when immigration is a hot issue for the US presidential campaign

Republican presidential candidate Donald Trump has criticized the pope's plan to visit the border wall that separates Ciudad Juarez from El Paso, Texas, to put a focus on the plight of migrants.

Trump said in an interview with Fox that he did not think the pope understood the danger to the US of an open border with Mexico. "I think Mexico got him to do it because they want to keep the border just the way it is. They're making a fortune, and we're losing," he said.

On Tuesday, Vatican spokesman Federico Lombardi responded, saying: "The pope always talks about migration problems all around the world, of the duties we have to solve these problems in a humane manner, of hosting those who come from other countries in search of a life of dignity and peace."