With military service members standing at attention on Tuesday, Carter's flag-draped casket was carried from Air Force One to a hearse embossed with the presidential seal.
The motorcade was due to travel to the US Navy Memorial on Pennsylvania Avenue, where his remains will be transferred to a horse-drawn caisson for a funeral procession to the Capitol.
The state funeral for the 39th US president on Thursday coincides with preparations for Republican President-elect Donald Trump to succeed Democratic President Joe Biden. Security in Washington is higher than usual.
The Capitol, where Carter will lie in state, is surrounded by miles of fencing ahead of Trump's January 20 inauguration.
Carter, a Democrat who served one White House term from 1977 to 1981, died December 29 at the age of 100.
Former US President Jimmy Carter was awarded the Nobel Peace Prize in 2002. (AP PHOTO)
The former Georgia peanut farmer struggled with a bad economy and the Iran hostage crisis while in office and was handily defeated for re-election by Republican Ronald Reagan.
In the decades since, he earned a reputation as a committed humanitarian and is widely seen as a better former president than he was a president. He was awarded the Nobel Peace Prize in 2002.
Carter lived longer than any other US president and had been in hospice care for nearly two years before his death. His last public appearance was at wife Rosalynn's funeral in November 2023, where he used a wheelchair and appeared frail.
In August, his grandson Jason Carter said Carter was looking forward to casting a ballot for Democratic presidential candidate Kamala Harris, who lost to Trump.
Biden has ordered flags at government buildings to be flown at half-staff for 30 days as a sign of mourning. That has irked Trump, who has said they should not be lowered during his inauguration.
At a news conference, Trump reiterated his desire to take back control of the Panama Canal, which Carter signed over to Panama during his presidency.
Members of Congress will pay their respects at a service in the Capitol Rotunda.
Carter will lie in state in the Rotunda with a military guard of honour for 24 hours. His body will then travel by motorcade to the Washington National Cathedral.
Both Biden and Trump were expected to attend Carter's funeral service on Thursday.
Biden was expected to deliver the eulogy at the service.
After that, Carter's remains will be flown back home to Georgia. His body will be interred later that day in his hometown of Plains.
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