The third-largest mosque in the world officially opened in Algiers on Sunday, 16 years after the German firms of KSP Jürgen Engel Architekten and Krebs und Kiefer won the competition to design it.

The Djamaa el Djazaïr, as the mosque is called, was officially inaugurated by President Abdelmadjid Tebboune, although construction was completed in 2019 and the site has been open to international visitors since then.

The mosque is built on a 28ha site overlooking the Bay of Algiers. Its prayer hall is 2ha in size and is surrounded by 618 octagonal columns and topped by a 50m-diameter dome.

This is able to accommodate as many as 120,000 worshippers at one time. The only mosques larger are the Great Mosque of Mecca and Al-Masjid an-Nabawi of Medina.

The minaret of the mosque reaches 265m, making it the tallest building in Africa. As well as the muezzin, it houses a 37-storey observation deck giving a view over the whole of the Algerian capital. The walls contain 6km of ornate writing that was engraved by laser.

The design is based on a traditional colonnade-style building with North African flourishes to honour the Algerian tradition – as well as a helicopter landing pad and a library that can house up to one million books.

The $900m project was carried out by China State Construction Engineering Corporation, which has also built a motorway and around a million homes in Algeria.

The project manager was Canadian firm Dessau-Soprin, and French consultants Socotec and Egis helped with engineering design and construction supervision.