Knock has become a popular destination for pilgrims
A crowd of about 7,000 people turned up at a County Mayo pilgrimage shrine on Saturday after being told that the Virgin Mary was to appear.
Dublin man Joe Coleman, who claims to be a visionary, predicted that the apparition would take place at Knock at 1500 GMT.
Mr Coleman left the shrine claiming he had just witnessed an apparition but said he could not yet reveal details.
He told the Irish Times on Friday that up to 50,000 people would turn up.
Mr Coleman said the vision would only be visible to people who came "with an open heart".
Earlier this month, about 5,000 people arrived at Knock Shrine after a similar prediction by him.
The Archbishop of Tuam, Dr Michael Neary issued a statement earlier this week clarifying the church's view of Mr Coleman's predictions.
"It is not healthy, does not give glory to God and . . . is not good witness to the faith to be looking for extraordinary phenomena," Dr Neary said.