Cardinal Cahal Daly is seriously ill in hospital.
The 92-year-old retired cleric was taken from his home in south Belfast after suffering heart problems.
It is understood Cardinal Daly was being treated at the City Hospital’s coronary care unit.
“The Cardinal is in Belfast City Hospital,” a Catholic Church spokesman said.
Cardinal Daly was born in 1917 and ordained a priest in 1941.
He was appointed Bishop of Ardagh and Clonmacnoise in 1967 and installed as Archbishop of Armagh in 1990. A year later he was created Cardinal.
He retired in October 1996, when Cardinal Sean Brady took over the role, and returned to his study of philosophy.
Cardinal Daly is renowned for a being a prolific book writer and has had many philosophical papers published.
He is also highly regarded for his work with Irish Bishops on the New Ireland Forum in the 1980s and leading a delegation on the Forum for Peace and Reconciliation in the 1990s, both of which were set up to explore ways of ending violence in the North.