SANAA has been selected to design a new building for Art Gallery NSW in Sydney, ahead of architects including Kengo Kuma, David Chipperfield, Renzo Piano and Herzog & de Meuron.

The Japanese firm, which is led by architects Kazuyo Sejima and Ryue Nishizawa, saw off competition from 11 established studios to win the commission for the new landmark building at one of Australia's most important art galleries.

The new building will take over two sites to the north of the existing Art Gallery NSW building – one that overlooks a motorway and one currently occupied by second world war oil tanks.

Set to open in 2021, in time for the institution's 150th anniversary celebrations, the structure is envisioned as a series of pavilions that cascade towards Sydney Harbour and frame a new public plaza.

"The subtle profile of the pavilions complements and preserves the dignity of the existing gallery building, creating spaces to bring people together and foster a sense of community, imagination and openness," said the competition organisers.

"The concept looks towards the future, thinking about how audiences will experience art in Sydney as we transform the gallery for the 21st century."

The expanded facility will more than double exhibition space for the gallery's permanent collection, which includes contemporary art from Australia and abroad, historical art from the Asia Pacific region, and Aboriginal art and artefacts.

It will also create temporary exhibition space, education rooms, an expansive research archive, and cafe and restaurant facilities.

Twelve offices were initially invited to submit their ideas for the contest, and were later cut back to a shortlist of five: SANAA, Kengo Kuma & Associates, Kerry Hill Architects, RMA Architects and Sean Godsell Architects.

The winner was selected by a jury including Art Gallery NSW director Michael Brand, and architects Toshiko Mori, Glenn Murcutt and Juhani Pallasmaa.

Sejima and Nishizawa will now spend 12 months developing a detailed design, with the aim to submit a planning application in mid 2016.