Lisbon's mayor has been sharply criticised on Portuguese social media after it was revealed his office would spend over £4.4m (5 million euros) to build an altar for Pope Francis to celebrate a mass at this year's World Youth Day.

The Portuguese capital will host the international festival from from 1st-6th August bringing together the Pope and hundreds of thousands of young Catholics from all over the world.

Observador newspaper reported on Tuesday the mayor's office had hired the country's largest construction company, Mota-Engil, to build the altar for £3.7m (4.2 million euros). Details of the deal were published on an official database for public contracts.

Foundations needed for the altar's roof, to be built by Oliveiras S.A, will cost an extra  £880,440 (1 million euros), according to the contract.

"The specifications for the stage were defined in meetings we had with World Youth Day, the Church and the Holy See," said Lisbon's mayor Carlos Moedas, acknowledging it was a "very expensive" project.

But, at a time of soaring inflation, thousands were quick to take to social media to point a finger at Moedas, a former EU commissioner, for spending such a large amount on an altar.

"If the housing crisis was an altar for World Youth Day, it would already be solved," Fabian Figueiredo, from the Left Bloc party, said on Twitter. "The problem is not lack of money but spending priorities."

Rent prices in Lisbon have jumped 53 per cent since 2017, according to the National Institute of Statistics, but salaries remain low, with recent data from the Labour Ministry showing more than 50 per cent of workers made less than £880 (1,000) euros per month last year.

"As a Catholic and a man of faith I am saddened by this display of unnecessary opulence at such a difficult time," wrote Twitter user Manuel Barbosa.

Portugal's President Marcelo Rebelo de Sousa, a Catholic himself, said the altar would be used for other events in the future.