A quarter of a million Catholic pilgrims will begin flocking to the shrine at Fatima today to attend the opening of one of the world’s largest churches.

Costing €80 million (£54 million) and financed by an estimated five million annual visitors, the new Church of the Holy Trinity can accommodate nearly 9,000 worshippers. Access to its cavernous 12,000sq m (130,000sq ft) interior will be through 13 bronze doors, symbolising the number present at the Last Supper.

In contrast, the average congregation size in British churches is 100 and the average seated capacity in a parish church is 500. St Paul’s Cathedral can seat a congregation of up to 2,500

Pope Benedict XVI will send a live televised message to the gathered faithful on Sunday, the 90th anniversary of the last time that the Virgin of Fátima was reported to have appeared before three Portuguese shepherd children, delivering a series of apocalyptic visions of the future. The National Republican Guard, the country’s paramilitary police, will have 300 officers and 150 paramedics on hand.

Five million people a year travel to Fátima, 110 km (70 miles) north of Lisbon, and the numbers are rising as “faith tourism” becomes big business.

Local church officials had long complained that the existing basilica was far too small. Pilgrims should not be disappointed with its successor. It comes equipped with five chapels, nearly 50 confessional booths and a café for worshippers to “rest and reflect”. The oval building has no internal columns to avoid obstructing live television broadcasts. Computers will keep lighting levels constant and solar panels will provide energy.

The church includes a 500sq m mural of New Jerusalem made of thousands of handmade Portuguese tiles. The walls will bear passages from the Bible in 23 languages.

“I thank God I have not had to worry about money,” said Monsignor Luciano Guerra, the rector of the sanctuary. Even holy projects can be bedevilled by delays and cost overruns: the church was originally to cost €40 million and open its doors on May 13.

Alexandros Tombazis, the Greek Orthodox architect responsible for design, has described his new church as humble. He said that he made it relatively low-slung to avoid overshadowing the Basilica of Fátima.

The cult of Fátima began after three children claimed that the Virgin Mary appeared before them on May 13, 1917. In a series of visions over the following six months, the Virgin of Fátima allegedly revealed to them the “Three Secrets of Fátima”.

The first two were made public but the third was jealously guarded by the Catholic Church for decades, giving rise to fervent speculation and conspiracy theories. Because the “third secret” remained undisclosed, it was assumed that it described the end of the world. However, Pope John Paul II said that it referred instead to a “bishop in white” falling in a hail of bullets, which he took to be a prediction of the 1981 attempt on his own life. He attributed his narrow escape from death to the intervention of the Virgin Mary, and donated the bullet extracted from his abdomen to the Fátima shrine.

In 2000 he beatified two of the young shepherds, Francisco Marto and his sister Jacinta, who died in childhood. Their cousin Lúcia, who became a nun at Coimbra, died two years ago. At Fátima John Paul also revealed the long-awaited third secret of Fátima, which Sister Lúcia had confided to the Vatican. The first two “secrets”, which were published, referred to the world wars of the 20th century and the reconversion of communist Russia to Christianity.

In April Cardinal Tarcisio Bertone, the Secretary of State (Vatican Prime Minister) who will officiate at the inauguration ceremony this weekend, denied that the Vatican had withheld a fourth secret.

In a book recounting his conversations with Sister Lúcia he quoted her as telling him: “Everything has been published. No secret remains.”

Church of the Holy Trinity

8,600 worshippers

3.2 tonnes weight of bronze doors

£54m to build

125m (410ft) diameter

18m (60ft) high

13 entrances

500m² (5,382 sq ft) presbytery, the biggest in the world

Source: La Stampa

Great and good

— The Basilica of Our Lady of Peace, Yamoussoukro, Ivory Coast, is the world’s largest church. Its area is 30,000sq m(323,000sq ft)

— The dome of St Peter’s Basilica, Rome, reaches 119m (390ft)

— The Basilica of the National Shrine of Our Lady of Aparecida, Brazil, is the biggest church in the Americas. It has a volume of 1.2 million cu m (42 million cu ft)

— Münster Cathedral, Germany, is the world’s tallest church, at 162m

Sources: Encyclopaedia Britannica; sacred-destinations.com; stjohndivine.org; activitaly.it; praisebuildings.com