A "Catholic flashmob" at a wedding in Ireland has captured the attention of thousands with a video going viral on social media.

The delighted bride Patricia Doogan was amazed when her uncle, Irish celebrity Daniel O'Donnell, led members of the congregation in a rendition of 'How Great Thou Art' at their wedding ceremony.

Singers Derek Ryan, Tony Kenny, Shaun Cuddy, Tony Allen joined O'Donnell to lead the congregation in the song, to the surprise of the Donegal bride and her husband, Neil Swan.

Even the parish priest, Father Pat Ward, joined in, finishing off the performance with a falsetto.

"It was a total surprise," Patricia told the Independent.ie after the service. "The only two people who knew were my friend Gavin who was one of the singers and my sister Fiona who was bridesmaid. It was a huge surprise to everyone else at the church.

"Apparently there wasn't an actual rehearsal, just a gathering in the church before the mass began to discuss it. We had the best day ever and absolutely everybody said that the church was their favourite part of the day."

A video of the event was posted on Facebook Fr Ward and has been viewed more than 134,000 times.