Dublin police are building a temporary morgue ahead of Pope Francis's visit to Ireland later this month, as the hundreds of thousands of worshippers planning on attending the outdoor papal Mass have been warned of the risk of infection.

The papal Mass will be celebrated in Phoenix Park, Dublin on Sunday, August 26 with half a million expected to attend.

Health officials have warned that the event, set to be Ireland's biggest in 40 years, poses 'unique health risks to attendants'.

Risk: Pope Francis, pictured yesterday during his weekly general audience in Vatican City, is due to lead mass in Dublin on August 26, with more than 500,000 expected to attend

The temporary infrastructure being built in the park will also include a morgue, as there are fears that due to the significant number of elderly people in attendance, some may die of natural causes during the event, Irish media reports.

Officials have warned attendees to check their vaccines are up to date to avoid catching infectious diseases including influenza, mumps, hepatitis.

Dr Mary O'Riordan of Ireland's Health and Safety Executive said: 'Given the nature of this historic papal visit, a large number of young children and elderly visitors are expected to attend the final Mass, including many international visitors.

'In the current context of ongoing measles spread in Europe, it is highly advisable that all attendants, especially young children, ensure that they are up to date with their vaccinations.

She added: 'Outbreaks [at events] most commonly involve vaccine-preventable diseases such as measles, influenza, mumps and hepatitis.

'Other reported outbreaks are mainly of gastrointestinal infections caused by a number of different pathogens.'

The pope is visiting Ireland for two days to coincide with the World Meeting of Families.

In what is being called the country's biggest event in 40 years, the papal Mass will be celebrated in Phoenix Park, Dublin on Sunday August 26. Pictured: Mass at the Vatican

Held every three years, this major international event brings together families from across the world to celebrate, pray and reflect upon the central importance of marriage and the family.

Organisers believe it will be the largest single event the country has hosted since Pope John Paul II visited in 1979.

Rail operator Iarnrod Eireann has laid on extra services on all main routes to the capital and advance booking is mandatory.

Extra trains will operate from Cork, Kerry, Limerick, Galway, Mayo, Sligo, Rosslare and Waterford to and from Dublin.

The rail company said intercity train tickets will not be available for sale on the day and there will be no access for anyone who does not have a ticket or reservation.

Pope Francis greets the crowd from the popemobile during a weekly general audience at St Peter's square

Holders of tickets to the papal Mass can travel free of charge from some commuter destinations.

An Iarnrod Eireann spokesman said: 'We are looking forward to playing a major role in bringing customers to and from the World Meeting of Families events.

'The Phoenix Park Mass is the largest single event the country has hosted since Pope John Paul II visited in 1979.'

There will also be special rail services from Westport, Ballina and Athlone to/from Claremorris for the Pope's Knock shrine event on August 26, including a free bus transfer.