Cardinal Antoine Kambanda has called upon Christians to join Pope Francis and the whole universal church in prayer for Pope Emeritus Benedict XVI.

On Thursday, December 29, Kambanda tweeted, "The Church family of God, which is in Rwanda, in communion with Pope Francis and the entire Universal Church, prays to God through the intercession of the Virgin Mary, for Pope Emeritus Benedict XVI and all the people who take care of him.”

Kambanda made this call after Pope Francis asked for prayers for his predecessor, Benedict, on Wednesday, saying he is "very sick”.

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Benedict, who is 95, became the first leader of the Catholic Church to stand down in 600 years in 2013, citing advanced age.

The Vatican said the former pope’s health had worsened in recent hours. "The situation at the moment remains under control, constantly followed by doctors,” said spokesman Matteo Bruni.

Pope Francis was addressing a general audience in the Vatican’s Paul VI hall when he looked up from a piece of paper and spoke about Benedict’s declining health.

He then made the short trip from the hall to the Vatican Gardens to see Benedict at the Mater Ecclesiae monastery, where he has lived since he stepped down.

Earlier this month, Francis revealed he frequently visited his predecessor.

The former pope has struggled with speech for some time and two years ago a Maltese cardinal said Benedict had told new cardinals that "the Lord has taken away my speech to let me appreciate silence.”

Cardinals around the world joined Pope Francis in praying for his predecessor. "In these difficult and serious moments, let us unite in fervent prayer for our dear Pope Emeritus,” wrote Guinean Cardinal Robert Sarah, the most senior African prelate at the Vatican until last year.

When the Pope took new cardinals to meet him at the Mater Ecclesiae monastery in August, Benedict looked frail but he shook them all by the hand and engaged with them.