Former US President George HW Bush has died at the age of 94, his son George W Bush has announced.

George Bush Sr, as he was known, passed away on Friday evening, a spokesperson said on behalf of the family.

He was the 41st US president between 1989 and 1993, after serving two terms as vice-president to Ronald Reagan.

In April, he was admitted to a hospital intensive care unit with a blood infection, a week after the death of his wife of 73 years, Barbara.

Jeb, Neil, Marvin, Doro, and I are saddened to announce that after 94 remarkable years, our dear Dad has died," George Bush Jr, who went on to serve as the 43rd US president, said in a statement.

"[He] was a man of the highest character and the best dad a son or daughter could ask for."

On Twitter, US President Donald Trump paid tribute to his fellow Republican's "essential authenticity, disarming wit, and unwavering commitment to faith, family and country."

Despite achieving popularity ratings of 90%, Bush was accused of neglecting domestic affairs and was defeated by Bill Clinton in the 1992 election.

He had joined politics in 1964 after starting a Texan oil business and becoming a millionaire by the age of 40.

During World War Two, he was an aviator against the Japanese before being shot down in September 1944 while on a bombing raid.

He is survived by five of his children and their spouses, 17 grandchildren, eight great-grandchildren and two siblings.