Former US first lady Barbara Bush, the only woman to see her husband and son both sworn in as president, died on Tuesday, the Bush family said. She was 92.

Bush was the wife of the 41st president, George H.W. Bush, and mother of the 43rd, George W. Bush.

The Bush family had said in a statement on Sunday that she was in failing health, had decided not to seek further medical treatment and instead would focus on "comfort care."

According to some media reports, Bush had been battling chronic obstructive pulmonary disease and congestive heart problems in recent years.

Bush was dubbed "The Silver Fox" by her husband and children. She was known for her snow-white hair and for being fiercely protective of her family.

She was first lady when her husband was in the White House from 1989 to 1993. Her son, Republican George Walker Bush, triumphed in the disputed 2000 US election and was president from 2001 to 2009. The father-and-son presidents were sometimes referred to as "Bush 41" and "Bush 43."

The Bushes celebrated their 73rd wedding anniversary in January.

"She will be long remembered for her strong devotion to country and family, both of which she served unfailingly well," President Donald Trump and his wife, Melania, said in a statement that noted Bush's championing of literacy "as a fundamental family value."