The vigil began Wednesday night after Priscilla Presley and her daughter made the unscheduled and impromptu appearance on a stage set up just inside the walls of Graceland, Elvis' Memphis mansion. Together they briefly thanked the crowd for their undying admiration of the rock 'n' roll icon.
It was the first time both women had appeared together at the annual gathering, which became an official event in 1980.
Priscilla said the sight of thousands of fans holding up candles in tribute to Elvis was amazing.
"This is something that Elvis would never, ever have believed could have taken place here," said the actress and businesswoman, who was divorced from Elvis Presley in 1973.
Lisa Marie Presley, on the stage alongside her mother, told the fans she loved them for their devotion to her father. She also acknowledged she had shied away from making public appearances at past anniversary vigils.
"I've always avoided this because I felt that it would be too emotional, but I really felt it was important to come down here tonight," the singer's daughter, herself a singer-songwriter, told the crowd. "I love you very, very, very much."
Elvis admirers from around the United States and the globe have flocked each anniversary to Graceland, where the singer, a native of Tupelo, Miss., is buried. Presley died on Aug. 16, 1977, from a heart attack after battling prescription drug abuse. His abrupt death at 42 shocked legions of fans still mesmerized today by his singing, sex appeal and on-stage charisma.
The vigil, which runs through Thursday morning, marked the high point of Elvis Week, the annual celebration of Presley's life and career. Organizers said about 75,000 people were expected by authorities to take part in the vigil.
Those who participated in the procession moved up the tree-lined driveway to the right of the mansion, where the gravesite is located near a swimming pool. Heart-shaped wreaths made of red and white flowers lined the entrance to the site.
Mourners walked slowly through the tomb area, the candlelight casting shadowy figures against a stone wall.
Some teary-eyed mourners laid flowers on the gravesite, where Presley's father Vernon, mother Gladys, and grandmother Minnie Mae Hood Presley also are buried.
Outside, some fans used chalk to draw pictures of Elvis's face on the street, where groups of fans set up folding chairs to wait for the line to die down.
Sergio Galleguillo, of Santa Cruz, Argentina, said he became emotional when he walked past the graves.
"I felt the spirit of Elvis there, as if he was alive," said Galleguillo, who was making his first visit to the United States. "It really was a beautiful experience."
The somber atmosphere of the vigil was in contrast to some lighter moments beforehand.
As the line of people waiting to get into Graceland grew longer Wednesday evening, a group from a Brazilian fan club waved that nation's flag, danced and sang Presley's early-70s hit "Burning Love" in the street in front of the entrance.
Steps away, an Elvis impersonator, complete with a white-sequined jumpsuit and red sash, sat alone in the street in front of the entrance, lip synching "In the Ghetto."
Earlier in the day, Cheryl Skogen and friend Susan Struss held up black umbrellas with polka dots near the front of the line as they waited to enter Graceland's grounds. As longtime Elvis fans and neighbors in Los Angeles, they said they decided to come to Elvis Week without their husbands. They got up well before dawn Wednesday for a prime spot in the line.
Skogen said she first came to Graceland in 1981 before the home became a museum and a tourist attraction and has visited several times since. She remembers first seeing Elvis on "The Ed Sullivan Show" and being enthralled with his hip-swiveling performance at a Lack Tahoe concert.
"The first time I saw him he changed my life," said Skogen, now 66 and retired. "I had never seen anybody dance like he did or sing like he did or look like he did. He captured my heart."
A few spots down the line, Allen Black, 47, sat in a blue and white chair alongside the outer wall of Graceland. Black who is from Aurora, Colo., scene of the July 20 movie theatre shooting massacre said Elvis was a great performer but also someone who treated others well.
He talked about his memories of where he was when he first heard Elvis had died. He was 12 at the time.
"I was trying to record a song off the radio, and the news came on the radio, and I went to tell my dad," Black said, tears welling in his eyes. "He didn't believe me. It just stunned him."