Thousands of people filed through the central aisle of St. Peter's Basilica to pay their final respects to Pope Francis on Wednesday, the start of three days of public viewing ahead of the pontiff's funeral.

Throngs of ordinary faithful made their way slowly to the 16th-century basilica's main altar, where Francis' simple wooden casket was perched on a slight ramp, as four Swiss Guards stood at attention. Over the coming days, tens of thousands of people are expected to pass through the basilica, which is staying open until midnight to accommodate them.

Cardinals, meanwhile, met in private to finalize preparations for Saturday's funeral and plan the conclave to elect Francis' successor.

Francis died on Monday at age 88, capping a 12-year pontificate characterized by his concern for the poor and message of inclusion, but also some criticism from conservatives who sometimes felt alienated by his progressive bent.

Wednesday opened with the bells of St. Peter's tolling as pallbearers carried Francis' body from the Vatican hotel where he lived into the basilica in a procession through the same piazza where he had delivered what became his final goodbye. Francis made a surprise popemobile tour through the faithful on Easter Sunday, after being assured by his nurse he could despite his continued frail health from a bout of pneumonia.

Cardinal Kevin Farrell, who is running the Vatican temporarily until a new pope is elected, led the procession down the central aisle to the altar, with clouds of incense preceding him and the choir chanting the Litany of Saints hymn. In pairs, cardinals in red cassocks approached the casket, bowed and made a sign of the cross, followed by small groups of purple-robbed bishops, black-clad ushers, priests and nuns - and then the doors were thrown open to the public.

Heads of state are expected for Francis' funeral, but the three days of public viewing in the basilica allow ordinary Catholics to grieve the Argentine pope. The viewing ends Friday at 7 p.m., after which Francis' casket will be closed and sealed.

Simplified rituals reflect Francis' wishes

Francis' death and funeral inaugurates a carefully orchestrated period of transition in the 1.4-billion strong Catholic Church, with cardinals gathering over the coming week before entering into a conclave, the secretive ritual voting in the Sistine Chapel to elect a new pope. There are 135 cardinals under age 80 and eligible to vote in the conclave, and the new pontiff will likely come from within their ranks. The conclave is not expected to begin before May 5.

Francis first lay in state in the Domus Santa Marta hotel in a private viewing for Vatican residents and the papal household. Images released by the Vatican on Tuesday showed Francis lying in an open casket, wearing the traditional pointed headdress of bishops and red robes, his hands folded over a rosary. The Vatican's No. 2, Cardinal Pietro Parolin, was pictured praying by Francis.

Once inside the basilica, Francis' casket wasn't put on an elevated bier - as was the case with past popes - but was just placed on an inclined ramp the main altar of the 16th-century basilica, facing the pews, with four Swiss Guards standing at attention by its side. It was in keeping with Francis' own wishes for all the rituals surrounding a papal funeral to be simplified and reflect the pope's role as a simple pastor, not a world leader.

"Look kindly, Lord, on the life and works of your servant, our Pope Francis," Farrell said from the altar. "Welcome him into the dwelling of perpetual light and peace and grant that your faithful people may follow fervently in his footsteps, bearing witness to the Gospel of Jesus."

Italian police have tightened security for the viewing and the funeral, carrying out foot and horse patrols around the Vatican, where pilgrims continued to arrive for the Holy Year celebrations that Francis opened in December. The faithful who walk through St. Peter's Holy Door are granted indulgences, a way to help atone for sins.

"For me, Pope Francis represents a great pastor, as well as a great friend to all of us,'' said Micale Sales, visiting St. Peter's Basilica from Brazil.

"I think he spread a positive message around the world, saying there shouldn't be any violence, there should be peace around the world,'' said Amit Kukreja, from Australia.

Planning for the conclave is now underway

The funeral has been set for Saturday at 10 a.m. in St. Peter's Square, and will be attended by leaders including U.S. President Donald Trump and Ukrainian President Volodmyr Zelenskyy.

Cardinals are continuing their meetings this week to plan the conclave to elect Francis' successor, make other decisions about running the Catholic Church as world leaders and the ordinary faithful grieve the pontiff's death.

History's first Latin American pontiff charmed the world with his humble style and concern for the poor but alienated many conservatives with critiques of capitalism and climate change. He last appeared in public on Sunday with an Easter blessing and popemobile tour through a cheering crowd in St. Peter's Square.

He had some reservations about looping through the square packed with 50,000 faithful, Vatican News reported on Tuesday, but overcame them - and was thankful that he had greeted the crowd. He died the next morning.

"The death of a pope is not a small thing, because we've lost our leader,'' said Julio Henrique from Brazil. "But still, in a few days, we will have a new leader. So ... the thing of hope remains. Who will assume Peter's throne?"