The most popular art gallery in the U.K. plans to open a new 10-storey extension next June – after a major revamp – costing $400 million at the Tate Modern.

The gallery is located in a former power station beside the Thames in London.

It opened in 2000 and welcomes more than 5 million visitors a year.

Architects Herzog and de Meuron designed the new building – which is linked to the existing structure by the gigantic Turbine Hall. The expansion will add 60 per cent more display space for the Tate Modern’s collection of contemporary and modern art.

And the renovation is also transforming the power plant’s former oil tanks into performance spaces.

Tate director Nicholas Serota says the gallery faces funding cuts from Britain’s government – but will fight to keep its policy of free admission.