Pope Francis has warned that some seminaries, churches and monasteries in Europe could be shut down in the future due to the shortage of priests and nuns.

During the annual assembly of the Italian bishops conference on Monday, Francis expressed concern about the "crisis of vocations" in Europe, which has seen the sharpest decline in the number of priests in recent years.

The latest statistics from the Vatican has shown that the number of priests in Europe fell by 2,502 between 2014 and 2015. In contrast, the priesthood has shown an increase in Africa and Asia, where the Catholic Church continues to grow.

Francis told the Italian bishops that the declining number of priests in Europe could be due to several factors such as demographic and cultural changes, as well as the scandals in the Church.

"How many seminaries, churches, monasteries and convents will be closed in the next few years? God only knows," the pontiff said, as reported by the Associated Press.

Despite the decreasing number of priests, the number of baptized Catholics has grown from 1.27 million to nearly 1.29 million worldwide.

The Pope previously suggested ordaining married men to the priesthood in areas suffering from priest shortages.

In an interview with the German newspaper Die Zeit last year, Francis said that the Church must consider the possibility of ordaining "viri probati" - married men of proven faith - as priests to minister to Catholics in remote communities.

The pontiff had warned that the priest shortage is an "enormous problem" and could weaken the Church "because a Church without the Eucharist doesn't have strength - the Church makes the Eucharist, but the Eucharist also makes the Church."

Francis, however, stressed that making celibacy an option for priests in training was "not the solution."

While most Catholic priests are expected to be celibate, some 23 Eastern churches that are in full communion with the Vatican allow members of the clergy to get married. 

In 2014, the Pope cited Anglican ministers who converted to Catholicism and Coptic Catholics as examples of married priests in the Church.

The Associated Press reported that the "viri probati" proposal would probably be discussed in an upcoming meeting of the world's bishops. One of the topics in the meeting scheduled to take place next year will reportedly focus on the Amazon region, where the ratio of priest to Catholics is 1 to 1,000.