Former United States President George H W Bush has fallen at home in the US state of Maine and broken a bone in his neck.

Spokesman Jim McGrath said that the 91-year-old Bush was in stable condition and is doing "fine" after Wednesday's fall.

He said in a tweet that the 41st president will be in a neck brace.

41 fell at home in Maine today and broke a bone in his neck. His condition is stable -- he is fine -- but he'll be in a neck brace. — Jim McGrath (@jgm41) July 16, 2015

Bush was hospitalised in Houston in December for about a week for treatment of shortness of breath. He said he was "grateful to the doctors and nurses for their superb care" after his treatment there.

Bush is the oldest living former US president. He served two terms as Ronald Reagan's vice president before being elected the nation's president in 1988.

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After one term highlighted by the success of the 1991 Gulf War in Kuwait he lost to Democrat Bill Clinton amid voters' concerns about the economy.

The father of fellow ex-president and namesake George W Bush and 2016 presidential contender Jeb Bush spent two months in hospital in 2012 and 2013, including a stretch in intensive care, for a bronchitis-related cough and associated fever.

Bush also suffers from Parkinson's disease, which has confined him to a motorised wheelchair in recent years.