A suspected arsonist has started a fire inside Barcelona's Sagrada Familia basilica, forcing hundreds of tourists to evacuate one of Spain's most popular attractions.
Four people were treated for smoke inhalation and the fire caused what appears to be significant damage to the sacristy, police said.
Around 1,500 people were evacuated from architect Antoni Gaudi's unfinished masterpiece. The towering basilica is one of the top draws in Spain, receiving more than two million visitors a year.
Tourists saw smoke coming from inside the sacristy, raised the alarm and the suspected arsonist was arrested.
The sacristy is where priests put on their vestments in preparation for Mass. The arsonist set fire vestments that were being stored there.
Police said he had a lighter and pieces of fabric that could be used to start a fire, and the fire itself caused significant damage, including a chair that was burned.
The Sagrada Familia was a church until it was consecrated as a basilica by the Pope during a visit to Barcelona in November.
Gaudi was a Catholic who largely dedicated his life to the project. Construction of the church began in 1882, and Gaudi died in 1926.