Dame Catherine, who was born into poverty, died one of Britain's wealthiest women at her home near Jesmond Dene, Newcastle upon Tyne, at 12.30pm, on Thursday.
The announcement was made by Anthony Shiel, who had been her agent since 1970.
He said her family were "desperately upset".
"It's very sad. She had been under the weather for the last few months. In a way it was not unexpected," said Mr Shiel.
"I know she had serious blood problems all her life and had suffered several haemorrhages.
![[ image: width=150]](/olmedia/110000/images/_111048_grab_of_cookson_books_on_rack_150.jpg)
"The last time I saw her was last summer and she was in perfectly good spirits.
"She was very weak and had lost a lot of weight but she was still laughing, joking and had retained full mental capacity."
Even though her first novel was not published until almost halfway through her life, Dame Catherine sold more than 100 million books in 30 different countries.
"She was a unique woman. I remember her most for the hard life she led, her zest and curiosity. She is irreplaceable," said Mr Shiel.
The success of her books, which centred mostly on the Tyneside she grew up in, remained undiminished by modern life.
She has rarely been out of the top ten most-borrowed books in British public libraries, and in 1997, for the second year running, nine out of ten out of the most popular library books borrowed were written by Dame Catherine.
After a childhood of poverty, a few weeks before her 84th birthday, a Sunday newspaper named her as Britain's 17th richest woman with an estimated fortune of £14 million.
Tyneside tributes
Tributes have been paid by those in the literary world and also from the area she called home.
Mark Barty-King, managing director of Dame Catherine's publishers Transworld, said: "We have lost not only a most prolific novelist but a very true and loyal friend.
Each book, she said was "remarkable for its sincerity and warmth".
"She will be greatly missed by all who knew her and by her millions of readers throughout the world."
Best-selling author Barbara Taylor Bradford praised the work of a fellow writer.
"I think she did what a novelist was supposed to do. She entertained, she brought human emotion to the paper."
The chairman of the Romantic Novelists' Association, Angela Arney said: "She was held in very high esteem. She didn't just write romantic novels but social history.
"I think everyone wanted to be like her. She encapsulated the spirit and the times of the period she wrote about."
Dame Catherine was revered on Tyneside, and South Tyneside Borough Council now markets itself as 'Catherine Cookson Country.'
The authority's leader described her as the area's "favourite and most famous daughter".
Councillor Paul Waggott said the death of Dame Catherine "leaves the borough with a sense of deep loss".
"Her death comes as a great shock to those who have known and admired her tremendous courage in battling against ill-health for many years. Our deepest sympathy goes out to her devoted husband Tom."
And the ordinary people of the area were equally sorry to hear the news.
She was described as "a wonderful woman", by some while others believed "everybody from the town will miss her dearly."
Next steps for peace
Blairs' surprise over baby
Bowled over by Lord's
Beef row 'compromise' under fire
Hamilton 'would sell mother'
Industry misses new trains target
Quins fightback shocks Cardiff
(From Sport)
Vodafone takeover battle heats up
(From Business)
IRA ceasefire challenge rejected
Thousands celebrate Asian culture
Christie could get two-year ban
(From Sport)
Colleagues remember Compo
(From Entertainment)
Mother pleads for baby's return
Toys withdrawn in E.coli health scare
Nurses role set to expand
(From Health)
Israeli PM's plane in accident
More lottery cash for grassroots
Pro-lifers plan shock launch
Double killer gets life
Cold 'cure' comes one step closer
(From Health)
Straw on trial over jury reform
(From UK Politics)
Tatchell calls for rights probe into Mugabe
Ex-spy stays out in the cold
Blair warns Livingstone
(From UK Politics)
Smear equipment `misses cancers'
(From Health)
Boyzone star gets in Christmas spirit
(From Entertainment)
Fake bubbly warning
Murder jury hears dead girl's diary
Germ warfare fiasco revealed
(From UK Politics)
Blair babe triggers tabloid frenzy
Tourists shot by mistake
A new look for News Online