Former US president George H W Bush has been in a Houston hospital since Saturday after he experienced shortness of breath, a family spokesman said on Wednesday.

Bush, who at 92 is the nation's oldest living ex-president, has “responded very well to treatments” at the Houston Methodist Hospital, spokesman Jim McGrath said in an email to Reuters.

“Doctors and everyone are very pleased, and we hope to have him out soon,” McGrath wrote.

Bush is the father of former President George W Bush and former Florida Governor Jeb Bush, who sought the 2016 Republican presidential nomination.

The elder Bush, a Republican like his sons, was vice president during Ronald Reagan's two White House terms before being elected president in 1988. He lost his reelection bid to Bill Clinton, then the Democratic governor of Arkansas, in 1992.

A naval pilot during World War Two, Bush became an occasional skydiver after leaving the presidency and marked his 90th birthday with a jump out of a helicopter.

He has used a wheelchair in his later years and was hospitalised twice in 2014, once for seven weeks with pneumonia and again for breathing difficulties. In July 2015, he broke a bone in his neck in a fall at the family home in Maine.

Bush's public appearances have been rare since he entered his 90s. Sitting in his wheelchair, wearing a brace on his neck and clad in a Houston Astros jersey, he tossed out the first pitch at the team's playoff game against the Kansas City Royals in October 2015.

In 2016, he marked the 75th anniversary of Japan's attack on Pearl Harbor by attending a ceremony at his library at Texas A&M University, where Bob Dole, the former Republican senator from Kansas, received an award for public service.