Three days of formal mourning for former first lady Nancy Reagan has begun.

Mrs Reagan's casket was taken in a police-escorted motorcade up an empty road for a public viewing at the Ronald Reagan Presidential Library.

The procession from Santa Monica passed beneath a large American flag on a stretch of normally congested road way and then turned onto the Ronald Reagan Freeway where firefighters saluted from atop fire trucks parked on overpasses and other observers held their hands over their hearts.

As the procession turned up the long, steep driveway to the library in the hills of Simi Valley, more than 100 people held small flags.

Members of the armed services carried the casket into the library, where daughter Patti Davis, dressed in black, was among about 20 family members and close friends who attended a short prayer service at the closed casket.

"May angels surround her and saints release her to Jesus," the Rev Stuart Kenworthy, vicar at the Washington National Cathedral, said during the 10-minute service.

The Rev Donn Moomaw, the Reagan family's pastor, read from the 23rd Psalm, which begins, "The Lord is my shepherd; I shall not want."

Attendees included the children of Ronald Reagan's son Michael and Dennis Revell, the widower of the president's late daughter Maureen. Michael Reagan and the president's other son, Ron Prescott Reagan, are expected at Friday's funeral.

After the private service, House Speaker Paul Ryan paid his respects, bowing his head in prayer aside the casket and making the sign of the cross.

The casket was covered in white roses and peonies, Mrs Reagan's favourite flowers.

Earlier, after a short private service at a Santa Monica funeral home, the casket was carried by pallbearers that included members of Reagan's Secret Service detail to a hearse for the final 45-mile journey to the hill country north-west of Los Angeles where two days of public viewing precede the funeral.

Several hundred onlookers stretched along the boulevard leading away from the Tudor-style funeral home.

"She was just a very classy woman, always," said Jeanie Maurello, a medical assistant at Providence St. John's Health Centre. "I thought she did a wonderful job. 'Just Say No' to drugs, she was behind all that."

She added: "There's always a great woman behind every great man."

Friday will be the funeral, which was planned down to the smallest details by the former first lady herself. Just as she was always by his side in life, Nancy Reagan will be laid to rest just inches from her husband on a hillside tomb facing west toward the Pacific Ocean.

Before her death at her Los Angeles homes on Sunday aged 94, she planned the funeral's flower arrangements, the music to be played by a Marine Corps band and the people who received invitations to the private memorial.

Among those who had RSVP'd for the service were former President George W Bush and his wife, former first lady Laura Bush; former first lady Rosalynn Carter; first lady Michelle Obama; and former first lady Hillary Clinton.

"No doubt about it, the most important of her special requests was that she be laid to rest right next to the president, as close as possible," said John Heubusch, executive director of the Ronald Reagan Presidential Foundation and Library.

The hour-long service, to which approximately 1,000 people have been invited, was to take place on the library's lawn.

Those with White House connections who have said they will attend include President Richard Nixon's daughter Tricia Nixon Cox and President Lyndon Johnson's daughters Lynda Bird Johnson Robb and Luci Baines Johnson. Other guests will include Katie Couric, Chris Matthews, Newt and Callista Gingrich, Anjelica Houston, Wayne Newton and actor Mr T, the Ronald Reagan Foundation said. Mr T was involved in Mrs Reagan's "Just Say No" anti-drug efforts during the 1980s.

Captain Christopher Bolt, commanding officer of the USS Ronald Reagan, will also be in attendance.