Tate Modern has unveiled plans to create a new, hyper-modernist 10-storey glass extension alongside its existing gallery, increasing the gallery's size by 60 per cent. The £165m project incorporates a 70 metre-high asymmetric "pyramidic" structure, resembling a huge staircase of cast-glass boxes, that its designers hope will become an "iconic new landmark for London".

The extension, containing several different-sized galleries, will create 7,000 square metres of new exhibition space and more educational facilities.

It will enable more of the Tate's collection to be brought out of storage, including large-scale video installations by Bruce Nauman and Bill Viola, and sculptures such as Louise Bourgeois' Giant Spider. Two performance areas will be created in the oil tanks of the former power station, which was decommissioned in the 1980s, including a 400-seat auditorium and performance space. The space will be left as "rough and authentic" as possible.

The entrance to the gallery will be changed so that the riverside front face of the building will become its rear, and a new entrance will be built on the south side. The new entrance will also open up a north-south pedestrian walkway through the gallery itself, which will be open for at least 12 hours a day.

The extension been designed by the Swiss architects Jacques Herzog and Pierre de Meuron, who built the Tate Modern, transforming the decommissioned power station on the South Bank site into London's biggest contemporary art gallery. Opened in 2000, it was built to receive 1.8 million visitors a year, but has become more popular than any gallery or museum in Britain, drawing four million a year.

Sir Nicholas Serota, the Tate's director, said the new space would enable the gallery to showcase more exhibitions from further afield, including Africa and Asia. He said he was confident the design would be well received. "One of the disappointments of the millennium was that there were no new modern buildings. It would be a sad city if it found itself in a position where the only new buildings were commercial ones," he said.

The Tate hopes the venture, which includes a £7m grant from the London Development Agency, will be ready in time for the London Olympics of 2012. Trustees intend to apply for National Lottery funding.

It is hoped the reversal of the Tate Modern's entrance will help to regenerate south Southwark. Nick Stanton, Southwark council leader, said: "We need to attract people further down, not just by the riverfront.What I particularly welcome with the plans is theemphasis on the community and on community space."

Ken Livingstone, the Mayor of London, said: "I am delighted the new development will enable Tate to accommodate more and more audiences, expand its educational programme, and play a key role in the regeneration of the surrounding area."

A decision on planning approval of the gallery designs is expected next spring.

Architects with a global reputation

Jacques Herzog and Pierre de Meuron are best known for designing the Tate Modern. They won the Pritzker Architectural Prize in 2001, which is considered the profession's Nobel Prize.

Their partnership, Herzog & de Meuron, was founded in Basle in 1978. It employs nearly 200 architects who are currently working on 40 projects worldwide. This year, The New York Times Magazine called it one of the most admired architectural firms in the world. It is responsible for the recently opened De Young Museum in San Francisco, and current projects include the National Stadium for the 2008 Olympics in Beijing and the Philharmonic Hall in Hamburg.

Sir Nicholas Serota, director of the Tate, said the gallery's new developmentwas a unique opportunity for a world-renowned architectural partnership to add to their own work.

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