Evangelist Franklin Graham is asking people to pray for former U.S. President George H. W. Bush and his family after he was rushed to the hospital due to an acute respiratory problem stemming from pneumonia.

"As I am on my way to Washington for the inauguration, will you join me in praying for the Bush family? Former President George H.W. Bush was hospitalised over the weekend and is in ICU, and now Mrs. Bush has been taken to the hospital," he wrote on his Facebook page. "My parents counted this special couple as close friends over the years and enjoyed vacationing with them in Kennebunkport."

Graham's appeal for prayer appeared to have produced good results since a family spokesperson later told CNN that Bush and his wife are now "both on the upswing" after being admitted to the hospital.

Spokesman Jim McGrath said on Thursday, "They may not be out of the woods yet, but we can see the edge of the forest."

Barbara continues to be treated for her bronchitis with antibiotics, but McGrath said she feels "a thousand percent better today."

As for Bush, he remains in the intensive care unit, but is alert and remains in stable condition. He is actively being evaluated before having his breathing tube removed.

"He is doing better — of course he has a ways to go — but it's hard not to be encouraged," McGrath said.

Because of his fragile health condition, Bush wrote a letter to Donald Trump and issued an apology since he would be missing the latter's inauguration ceremony. He and his wife wished Trump "the very best as you begin this incredible journey of leading our great country."

"My doctor says if I sit outside in January, it likely will put me six feet under. Same for Barbara," Bush wrote. "So I guess we're stuck in Texas."