US President Donald Trump and first lady Melania Trump will be among the mourners Wednesday at the state funeral in Washington for former US President George HW Bush.

Trump will join four former US presidents and their wives for the funeral at Washington National Cathedral. Bush, the 41st US president, died at his Houston, Texas home on Friday at the age of 94.

Eulogies are to be given by Bush's son, former president George W Bush, former Canadian prime minister Brian Mulroney, former US senator Alan Simpson and presidential historian Jon Meacham, according to news reports.

Trump, who called fellow candidate Jeb Bush, a son of George HW Bush, "weak" and "low energy" during the 2016 presidential campaign, is not scheduled to speak, according to news reports.

He and first lady Melania Trump paid their respects at the US Capitol, where Bush lay in state, on Monday evening and met Tuesday evening with George W Bush, his wife Laura and other members of the Bush family.

All three other living former US presidents - Jimmy Carter, Bill Clinton and Barack Obama - and their wives are scheduled to attend the funeral. Former first ladies Rosalynn Carter, Hillary Clinton and Michelle Obama also will attend.

Among the foreign leaders among the mourners will be German Chancellor Angela Merkel, who called Bush a "stroke of luck in German history" and praised his role in transatlantic relations.

Bush, a strong backer of German reunification during his time in office, served between 1989 and 1993, presiding over the end of the Cold War.

Prince Charles of Britain, former British prime minister John Major, King Abdullah II and Queen Rania of Jordan, 
Australian Governor General Peter Cosgrove and his wife Lynne and Polish President Andrzej Duda are to attend, according to a list provided to media by Bush spokesman Jim McGrath.

Former leaders of Japan, Qatar, Portugal, Estonia, Poland Kuwait and Bermuda also will be among the mourners, a Bush family spokesman said.

The former president's funeral is scheduled to begin at 11 am (1500 GMT) after the casket carrying Bush's body is transported in a motorcade from the Capitol to the cathedral.

Trump proclaimed Wednesday a national day of mourning and issued an executive order closing the federal government in honour of Bush. US financial markets also will be closed.

The US military along with law enforcement authorities in Washington are in charge of the funeral. Nearly 4,000 military and civilian personnel from all branches of the US armed forces are responsible for the ceremonies, a news release issued by the military said.

"This state funeral is a culmination of years of planning and rehearsal to ensure the support the military renders President Bush is nothing less than a first-class tribute," said Major General Michael L Howard.

Military musical units along with colour guards and uniformed soldiers who will fire artillery to salute the deceased president, escort dignitaries and members of the Bush family and carry the casket.

Bush's body arrived Monday in Washington after a ceremony to honour him in Houston. The 747 jet assigned to the flights was temporarily recommissioned "Special Air Mission 41." Bush's remains will be flown back to Texas on Thursday for burial alongside his wife Barbara, who died in April.

The 41st president, who late in his life became known for wearing colourful socks, will be buried wearing socks that bear an image of five fighter jets ascending as a tribute to his lifetime of service, McGrath said on Twitter.

Bush is the last US president to have fought in World War II. He volunteered at age 18 in 1942, became a Navy pilot and flew 58 missions.