Antoni Gaudi's Sagrada Família in Barcelona is edging towards completion, with the team behind it hopeful they can put the finishing touches to the modernist basilica in around 10 years, more than a century after the famed architect's death.

The project's chairman, Esteve Camps, told reporters on Thursday he had learned to be cautious after the COVID pandemic caused a collapse in visitor revenues for one of Europe's biggest tourist draws and delayed the project's end beyond a 2026 goal.

"We cannot say whether it will be 10, 11 or 12 years … but we think that in normal circumstances, without obstacles, it is likely that in 10 years we could be finished."

Gaudi worked on the basilica from 1883 until he died in 1926. Next year, to mark a century since his death, the project's leaders hope to have finished the external aspects of its main 172.5-metre tower, dedicated to Jesus Christ, making it Barcelona's tallest building.

Once completed, the Sagrada Família will have three facades and 18 towers.

Pope Leo has been invited to lead a commemoration mass and opening ceremony of the tower next June. An answer from the Vatican is expected later this month, Camps said.

The project's current chief architect, Jordi Fauli, told Reuters the tower was already topping 155 metres and the lower half of a massive cross that will crown it has already been built.

Local authorities are yet to approve architects' plans to build a large staircase outside the Sagrada Familia's main gate which would likely mean demolishing at least one residential building and has triggered protests by neighbours.

Camps said he was confident the staircase would be approved though conceded the issue would require negotiations with the authorities and could end up in court if local opposition persisted.

The emblematic building is also, like much of Barcelona, at tourism saturation point. Last year, the number of visitors to the basilica hit a new record, reaching 4.9 million people. Officials say that even when completed, its maximum capacity cannot change.