Former US president Bill Clinton has praised Seamus Heaney as "our finest poet of the rhythms of ordinary lives" and a "powerful voice for peace".
The farmer's son who went on to become a world renowned Nobel laureate died in hospital in Dublin aged 74.
Mr Clinton and his wife Hillary said they were saddened to learn of the death of their "friend".
"Both his stunning work and his life were a gift to the world. His mind, heart, and his uniquely Irish gift for language made him our finest poet of the rhythms of ordinary lives and a powerful voice for peace. And he was a good and true friend," the Clintons said.
"We loved him and we will miss him. More than a brilliant artist, Seamus was, from the first day we met him, a joy to be with and a warm and caring friend - in short, a true son of Northern Ireland. His wonderful work, like that of his fellow Irish Nobel Prize winners Shaw, Yeats, and Beckett, will be a lasting gift for all the world."
Heaney was remembered by friends, contemporaries, admirers and politicians as a humble, warm, funny and open man as tributes flowed in from around the world. He is survived by his wife, Marie, and children, Christopher, Michael and Catherine Ann.
A funeral mass will take place on Monday at the Church of the Sacred Heart in Donnybrook, south Dublin followed by burial in his birthplace of Bellaghy, Co Derry.
Irish prime minister Enda Kenny said it would take Heaney himself to describe the depth of loss Ireland would feel over his death. "He is mourned - and deeply - wherever poetry and the world of the spirit are cherished and celebrated," he said.
The 1995 Nobel prize-winner was born in April 1939, the eldest of nine children, on a small farm called Mossbawn near Bellaghy in Co Derry, Northern Ireland, and his upbringing often played out in the poetry he wrote in later years.
Among the tributes, actor Adrian Dunbar led a round of applause at the bust of Heaney in the Lyric Theatre in Belfast. It will be followed with a celebration of Heaney's life on Saturday night, which will include readings of his work and personal tributes. Books of condolence are also to be opened at Belfast City Hall on Monday and the Guildhall in Derry city.