Barcelona's emblematic Sagrada Familia church finally has a completion date — 2026 or 2028, more than 140 years after it was started.

Joan Rigol, president of the committee charged with finishing the building by Antoni Gaudí, said it should be finished in time for the centenary for the architect's death – or, if not, two years later.

Five huge towers are being added to the eccentric building, which is among Spain's most-visited tourist attractions.

Gaudí died in 1926 after being runover by the city's No 30 tram. He had been living on the Sagrada Familia building site and looked so impoverished that it took several hours for doctors to realise who he was. The tram driver thought he had hit a drunken tramp.

Originally paid for by subscription, the church was always set to take a long time to build. "My client is in no hurry," Gaudí once said, referring to God.

The building was at one stage popularly known as "the cathedral of the poor" and Gaudi himself was known to go begging for contributions – which currently amount to around €500,000 (£440,000) a year.

An influx of tourists, along with modern masonry techniques, has seen work speed up considerably over the past two decades. Some three million fee-paying tourists are expected to visit this year alone, contributing €30m.

With a roof finally in place, Pope Benedict was able to consecrate it as a basilica last year. But a setback came when a man set fire to the basilica's sacristy in April, with repair work still under way.

"The damage is worse than we had thought," said the building's chief architect, Jordi Bonet. Authorities are now considering installing metal detectors at the entrance.

"Our new objective is to complete the six central towers, of which five have already been started," said Rigol.

The sixth tower will measure 170 metres and contain a lift to carry tourists to the top. Rigol added that a high-speed rail tunnel to be built nearby, which has been approved by the courts, may still damage the buildings foundations.

Bonet did not seem so sure about the finish date. "I'm not saying that it is wrong, I hope it is not, but it is not that simple. This is a very complex work and needs a lot of investigation," the architect told the RAC1 radio station. "Everyone has the best will, but I cannot give any assurances."