A single white rose was placed on the tomb that said "Franciscus" - the Pope's name in Latin. A light cast its warm glow over the tomb and a reproduction of the late pontiff's pectoral cross on the wall above it.
People filed past, many crossing themselves or snapping photos with their phones.
"Pope Francis for me was an inspiration, a guide," Elias Caravalhal said.
Caravalhal lives in Rome but was unable to pay his respects to Francis when he was lying in state in St Peter's Basilica after his death on Easter Monday at the age of 88.
He said he visited the tomb to bid farewell to the pontiff and "thank him for what he has done".
The tomb was opened on the second of nine days of official mourning for Francis, after which a conclave will be held to elect the next Pope.
No date has yet been set for the conclave, but it must start by May 10.
Cardinals who travelled to Rome for Francis's funeral will meet regularly this week ahead of the conclave as they start to chart a way forward for the 1.4 billion-strong Catholic Church.
Pope Francis chose his place of burial in St Mary Major Basilica, near an icon of the Madonna that he revered, because it reflects his "humble, simple and essential" life, the archbishop who administers the basilica said on Friday.
"It's unbelievable that he's no more with us," said Susmidah Murphy, who visited the tomb during a visit to Rome from her home in India.
"It's sad that we don't get popes like this very often."
