A £215m (US$329m, €296m) extension for London’s Tate Modern will open next year, the gallery’s director has said.

The announcement should assuage fears that construction work for the popular visitor attraction was running behind schedule. The designs have been on the table since 2008, and the extension was originally slated to open in time for the capital’s 2012 Olympic Games.

The 11-storey addition, designed by acclaimed architecture firm Herzog & de Meuron, will officially open on 17th June 2016, according to Sir Nicholas Serota, director of the Tate Modern.

The 65m-tall (213ft) building is set to add 21,500sq m (230,400sq ft) to the gallery's existing 35,000sq m (377,000sq ft), increasing the size of the attraction by 60 per cent, and two public spaces – a piazza and a child-friendly garden.