Roman Catholic cardinals will meet in a secret conclave to elect the new leader of the global Church starting from May 7, a senior Vatican source said on Monday.

Tens of thousands flocked to Santa Maria Maggiore Basilica — Pope Francis’s final resting place — in another testament to the popularity of the Argentine, who died aged 88 on Monday.

An energetic reformer who championed the poorest and most vulnerable, Pope Francis is credited with reinvigorating the Catholic Church’s appeal with his open, welcoming stance — a hard act to follow for whoever succeeds him.

All eyes turn now to the conclave, the secretive meeting of cardinals set to convene within days to elect a new pontiff.

Cardinals were to hold their fifth general meeting today since the pope’s death, at which they are expected to pick a date for the conclave.

On Sunday, most joined the crowds at Santa Maria Maggiore to attend an afternoon ceremony in tribute to the late pontiff.

The crowds were a testament to the popularity of Francis, an energetic reformer who championed the poorest and most vulnerable.

The date was decided during a closed-door meeting of cardinals at the Vatican, the first since the funeral of Pope Francis on Saturday, the source told Reuters today.

The official announcement is due shortly.

Some 135 cardinals, all under the age of 80 and from across the world, are eligible to take part in the conclave and decide who should be the next leader of the 1.4-billion-member Church.

The previous two conclaves, held in 2005 and 2013, lasted just two days.