The new Tate Modern © Hayes Davidson and Herzog & de Meuron.

LONDON (AFP).- London's Tate Modern gallery said Tuesday it will open its new extension on June 17 next year, a development which expands its display space by 60 percent. 

The gallery of international modern art, housed in a former power plant on the River Thames in London, is getting a new, 10-storey Switch House building shaped like a twisted pyramid. 

Already under construction, it was designed by the Swiss architects Jacques Herzog and Pierre de Meuron. 

"With 60 percent more display space, the world's most popular gallery of modern art will now feature over 250 artists from around 50 countries," said Tate. 

"It will reveal how art has evolved from the studios and salons where modernism was born to the live, interactive and socially-engaged projects happening around the world today." 

The gallery will undergo a complete re-hang, including works acquired since the gallery first opened in 2000. 

The total cost of the project, paid for by fundraising and government grants, is £260 million ($400 million, 360 million euros). 

Tate Modern is one of four Tate galleries around Britain. 

"Art is one of the most dynamic and engaged forms of human behaviour, and when people step into a museum today, they don't want to step out of their life, they want to get closer to it," said Tate Modern director Chris Dercon. 

"The new Tate Modern will be so much more than a container for art, it will be a platform for human encounters." 

Tate said in its annual report out Tuesday that 2014/15 was its best year for visitor numbers, with 7.9 million visits to its four galleries, 5.7 million of them at the Tate Modern. 

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