Barbara Bush, the snowy-haired president's wife whose plainspoken manner and utter lack of pretence made her more popular at times than her husband, U.S. president George H.W. Bush, died Tuesday. She was 92.

Family spokesperson Jim McGrath confirmed the death in a statement. The cause wasn't immediately known.

Bush brought a grandmotherly style to buttoned-down Washington, often appearing in her trademark fake pearl chokers and displaying no vanity about her white hair and wrinkles.

.<a href="https://twitter.com/FLOTUS?ref_src=twsrc%5Etfw">@FLOTUS</a> Melania and I join the Nation in celebrating the life of Barbara Bush: <a href="https://t.co/4OW72iddQx">pic.twitter.com/4OW72iddQx</a> —@realDonaldTrump

"What you see with me is what you get. I'm not running for president — George Bush is," she said at the 1988 Republican National Convention, where her husband, then vice-president, was nominated to succeed Ronald Reagan.

The Bushes, who were married Jan. 6, 1945, had the longest marriage of any presidential couple in American history. And Bush was one of only two presidential wives who had a child who was elected president. The other was Abigail Adams, wife of John Adams and mother of John Quincy Adams.

"I had the best job in America," she wrote in a 1994 memoir describing her time in the White House. "Every single day was interesting, rewarding, and sometimes just plain fun."

On Sunday, McGrath said Bush had decided to decline further medical treatment for health problems and focus instead on "comfort care" at home in Houston. She had been in the hospital recently for congestive heart failure and chronic obstructive pulmonary disease. In 2009, she had heart valve replacement surgery and had a long history of treatment for Graves' disease, a thyroid condition.

Our statement on the passing of Former First Lady Barbara Bush: <a href="https://t.co/MhTVYCL9Nj">pic.twitter.com/MhTVYCL9Nj</a> —@BarackObama

"My dear mother has passed on at age 92. Laura, Barbara, Jenna, and I are sad, but our souls are settled because we know hers was," George W. Bush said in a statement Tuesday. "Barbara Bush was a fabulous First Lady and a woman unlike any other who brought levity, love, and literacy to millions. To us, she was so much more. Mom kept us on our toes and kept us laughing until the end. I'm a lucky man that Barbara Bush was my mother. Our family will miss her dearly, and we thank you all for your prayers and good wishes."

A spokesperson says former president George H.W. Bush held his wife's hand all day and was by her side when she died.

Jean Becker, the chief of staff at Bush's office in Houston, said in a statement that the 41st president "is broken-hearted to lose his beloved Barbara."

Becker says it's a "very challenging time" for the 93-year-old Bush, but "he also is stoic and strong, and is being lifted up by his large and supportive family."

Former Canadian prime minister Brian Mulroney said in a statement: "A woman of great intelligence, conviction and kindness, Barbara Bush held no rancour for anyone, no matter how tough the political battles she may have endured. A great champion of literacy and children's education, Mrs. Bush made the world a better place"

Funeral services are planned for 11 a.m. Saturday at St. Martin's Episcopal Church in Houston, which she and her husband regularly attended.

According to a post on the George Bush Presidential Library Foundation website, Barbara Bush will lie in repose from noon to midnight Friday at the church for members of the public wishing to pay respects.

The funeral service Saturday is by invitation only.

Burial will be on the grounds of the Bush library at Texas A&M University in College Station, about 161 kilometres northwest of Houston.

U.S. President Donald Trump ordered U.S. flags flown at half-mast in her honour.

The publisher's daughter and oilman's wife could be caustic in private, but her public image was that of a self-sacrificing, supportive spouse who referred to her husband as her "hero."

Mia Trumble, 7, sits on Bush's lap after the former first lady spoke at a ceremony for Literacy Maine in Biddeford, Maine, in June 2011. (Robert F. Bukaty/Associated Press)

In the White House, "you need a friend, someone who loves you, who's going to say, `You are great,"' Barbara Bush said in a 1992 television interview.

Her uncoiffed, matronly appearance often provoked jokes that she looked more like the boyish president's mother than his wife. Late-night comedians quipped that her bright white hair and pale features also imparted an uncanny resemblance to George Washington.

Eight years after leaving the nation's capital, Bush stood with her husband as their son George W. was sworn in as president. They returned four years later when he won a second term. Abigail Adams was unable to share the experience: She died in 1818, six years before John Quincy Adams was elected.

'Ferociously tart-tongued'

Barbara Bush insisted she did not try to influence her husband's politics.

"I don't fool around with his office," she said. "And he doesn't fool around with my household."

In 1984, her quick wit got her into trouble when she was quoted as referring to Geraldine Ferraro, the Democratic vice-presidential nominee at the time, as "that $4 million — I can't say it, but it rhymes with rich."

"It was dumb of me. I shouldn't have said it," Mrs. Bush acknowledged in 1988. "It was not attractive, and I've been very shamed. I apologized to Mrs. Ferraro, and I would apologize again."

From left: Former first ladies Rosalynn Carter, Barbara Bush, Betty Ford, Nancy Reagan and then-Sen. Hillary Clinton are seen in January 2003. (Reed Saxon/Associated Press)

Daughter-in-law Laura Bush, another first lady, said Bush was "ferociously tart-tongued" from the start.

"She's never shied away from saying what she thinks ... She's managed to insult nearly all of my friends with one or another perfectly timed acerbic comment," Laura Bush said in her 2010 book, Spoken from the Heart.

In her 1994 autobiography, Barbara Bush: A Memoir, she said she did her best to keep her opinions from the public while her husband was in office. But she revealed that she disagreed with him on two issues: She supported legal abortion and opposed the sale of assault weapons.

Always a friend to Canada, Barbara Bush leaves a legacy of dignity, grace, service and devotion to family. Sophie and I send our deepest condolences to Presidents George H.W. and George W. Bush, their family, and to all Americans. —@JustinTrudeau

"I honestly felt, and still feel, the elected person's opinion is the one the public has the right to know," she wrote.

She also disclosed a bout with depression in the mid-1970s, saying she sometimes feared she would deliberately crash her car. She blamed hormonal changes and stress.

"Night after night, George held me weeping in his arms while I tried to explain my feelings," she wrote. "I almost wonder why he didn't leave me."

She said she snapped out of it in a few months.

Family woman

Mrs. Bush raised five children: George W., Jeb, Neil, Marvin and Dorothy. A sixth child, three-year-old daughter Robin, died of leukemia in 1953.

In a speech in 1985, she recalled the stress of raising a family while married to a man whose ambitions carried him from the Texas oil fields to Congress and then into influential political positions that included ambassador to the United Nations, Republican Party chairman and CIA director.

"This was a period, for me, of long days and short years," she said, "of diapers, runny noses, earaches, more Little League games than you could believe possible, tonsils and those unscheduled races to the hospital emergency room, Sunday school and church, of hours of urging homework or short chubby arms around your neck and sticky kisses."

This August 1992 photo shows the Bush family portrait in Houston, Texas. (Reuters)

Along the way, she said, there were also "bumpy moments — not many, but a few — of feeling that I'd never, ever be able to have fun again and coping with the feeling that George Bush, in his excitement of starting a small company and travelling around the world, was having a lot of fun."

In 2003, she wrote a follow-up memoir, Reflections: Life After the White House.

"I made no apologies for the fact that I still live a life of ease," she wrote. "There is a difference between ease and leisure. I live the former and not the latter."

Along with her memoirs, she wrote C. Fred's Story and Millie's Book, based on the lives of her dogs. Proceeds from the books benefited adult and family literacy programs. Laura Bush, a former teacher with a master's degree in library science, continued her mother-in-law's literacy campaign in the White House.

From left: Barbara Bush, George H.W. Bush, George W. Bush and Laura Bush are seen in April 2013 in Dallas, Texas. (Alex Wong/Getty Images)

The 43rd president was not the only Bush son to seek office in the 1990s. In 1994, when George W. was elected governor of Texas, son Jeb narrowly lost to incumbent Lawton Chiles in Florida. Four years later, Jeb was victorious in his second try in Florida.

"This is a testament to what wonderful parents they are," George W. Bush said as Jeb Bush was sworn into office. He won a second term in 2002, and then made an unsuccessful bid for the Republican presidential nomination in 2016.

Sons Marvin and Neil both became businessmen. Neil achieved some notoriety in the 1980s as a director of a savings and loan that crashed. Daughter Dorothy, or Doro, has preferred to stay out of the spotlight. She married lobbyist Robert Koch, a Democrat, in 1992.

Barbara Bush was a remarkable woman. She had grit & grace, brains & beauty. She was fierce & feisty in support of her family & friends, her country & her causes. She showed us what an honest, vibrant, full life looks like. Hillary and I mourn her passing and bless her memory. —@BillClinton

In a collection of letters published in 1999, George H.W. Bush included a note he gave to his wife in early 1994.

"You have given me joy that few men know," he wrote. "You have made our boys into men by bawling them out and then, right away, by loving them. You have helped Doro to be the sweetest, greatest daughter in the whole wide world. I have climbed perhaps the highest mountain in the world, but even that cannot hold a candle to being Barbara's husband."

'Cherish your human connections'

Barbara Bush was born Barbara Pierce in Rye, New York. Her father was the publisher of McCall's and Redbook magazines. After attending Smith College for two years, she married young naval aviator George Herbert Walker Bush. She was 19.

After the Second World War, the Bushes moved to the Texas oil patch to seek their fortune and raise a family. It was there that Bush began his political career, representing Houston for two terms in Congress in the late 1960s and early 1970s.

In all, the Bushes made more than two dozen moves that circled half the globe before landing at the White House in 1989. During the next four years, opinion polls often gave her approval ratings that exceeded her husband's.

George H.W. Bush poses with his wife Barbara during his campaign for Congress in the 1960s. (AFP/Getty)

The couple's final move, after Bush lost the 1992 election to Bill Clinton, was to Houston, where they built what she termed their "dream house" in an affluent neighborhood. The Bush family also had an oceanfront summer home in Kennebunkport, Maine.

After retiring to Houston, the Bushes helped raise funds for charities and appeared frequently at events such as Houston Astros baseball games. Public schools in the Houston area are named for both of them.

In 1990, Barbara Bush gave the commencement address at all-women Wellesley College, though some had protested her selection because she was prominent only through the achievements of her husband. Her speech that day was rated by a survey of scholars in 1999 as one of the top 100 speeches of the century.

"Cherish your human connections," Mrs. Bush told graduates. "At the end of your life, you will never regret not having passed one more test, winning one more verdict or not closing one more deal. You will regret time not spent with a husband, a child, a friend or a parent."