Britain's Maggie Smith, the double Oscar-winner who shone on stage and screen for more than seven decades, has died in hospital in London, her sons announced Friday, prompting a flood of tributes.

"It is with great sadness we have to announce the death of Dame Maggie Smith," Chris Larkin and Toby Stephens said in a statement.

"She passed away peacefully in hospital early this morning."

Over the course of her career, Smith won a Tony, two Oscars, three Golden Globes and five Baftas.

And she achieved late-career international fame for her depiction of the acerbic Dowager Countess of Grantham Violet Crawley in the hit television series "Downton Abbey".

Britain's King Charles III called her "a national treasure" who was admired around the world. Paying tribute to her "warmth and wit that shone through both on and off the stage", he posted a photograph of him sharing a joke with the actor.

Prime Minister Keir Starmer also called her a "true national treasure" while the Bafta TV and film academy saluted "a legend of British stage and screen".

Born in 1934 in Oxford in central England, the daughter of an Oxford professor of pathology, Smith made her stage debut in 1952 with the Oxford University Dramatic Society.

She won a best actress Oscar for the 1969 drama "The Prime of Miss Jean Brodie" based on Muriel Spark's novel, and best supporting actress for her role in the 1978 Neil Simon comedy "California Suite".

"An intensely private person, she was with friends and family at the end," her sons, both actors, said.

"She leaves two sons and five loving grandchildren who are devastated by the loss of their extraordinary mother and grandmother."

- 'One-of-a-kind' -

Famed for her scene-stealing charisma, Smith's long and successful career got started with a string of successes in London's West End and on Broadway in the 1950s.

She famously appeared opposite Laurence Olivier in an adaptation of Shakespeare's "Othello" in 1959.

This led to her joining Olivier's celebrated 1960s National Theatre company where she earned critical acclaim alongside her husband, the actor Robert Stephens.

Smith's marriage to heavy-drinking Stephens, with whom she had her two sons, collapsed in 1973 and they divorced two years later.

She remarried shortly after to the screenwriter Beverley Cross, who died in 1998.

Despite her serious acting reputation, Smith also appeared in lighter Hollywood hits such as 1992's "Sister Act" and the 1993 sequel "Sister Act 2".

Whoopi Goldberg, who starred in both films, wrote on Instagram: "Maggie Smith was a great woman and a brilliant actress.

"I still can't believe I was lucky enough to work with the 'one-of-a-kind'," she added.

UK actor Kristin Scott Thomas, who appeared alongside Smith in "My Old Lady" said her co-star "saw through the nonsense and razzmatazz" of acting.

"She had a sense of humour and wit that could reduce me to a blithering puddle of giggles. And she did not have patience with fools," she wrote on Instagram.

- 'Thank you, Maggie' -

In recent decades, some of her best-known films included "Gosford Park" (2001), "The Best Exotic Marigold Hotel" (2012) and "The Lady in the Van" (2015).

From 2001, her role as Minerva McGonagall in the "Harry Potter" films introduced her to a younger generation.

"Somehow I thought she'd live forever," Harry Potter author JK Rowling posted on X, formerly Twitter. "RIP Dame Maggie Smith."

Harry Potter star Daniel Radcliffe also paid tribute.

"I will always consider myself amazingly lucky to have been able to work with her, and to spend time around her on set," he said in a statement.

"The word legend is overused but if it applies to anyone in our industry then it applies to her. Thank you Maggie."

- 'Great genius' -

It was "Downton Abbey", which ran from 2010, that made her an international star again, unable to go out without being recognised.

"It's ridiculous," she told the British Film Institute in 2017. "I led a perfectly normal life until Downton Abbey.

"I would go to theatres, I would go to galleries and things like that on my own. And now I can't," she said.

Julian Fellowes, creator and writer of Downton Abbey, said Smith had a "marvellous instinctive grasp, she could make you cry your eyes out one minute and laugh like a drain the next without turning into someone different.

"I realised I was working with a great genius," he added.

Actor Hugh Bonneville, who played the son of the dowager duchess in the period drama, said: "Anyone who ever shared a scene with Maggie will attest to her sharp eye, sharp wit and formidable talent.

Smith was made a Dame of the British Empire in 1990 by Queen Elizabeth II.

© Agence France-Presse By Helen ROWE