London's Tate Modern art complex has unveiled plans to add a £215m glass building, which will increase the size of its exhibition space by 60%.
The South Bank is to be developed as "London's cultural quarter"
The site will combat overcrowding and give more than 4m visitors per year "the experience they seek and demand", said Tate director Sir Nicholas Serota.
An electricity sub-station will move to make way for the 11-floor extension.
Planning permission will be sought this autumn with the Tate hoping to open the building in time for the 2012 Olympics.
The project has been designed by architects Herzog and De Meuron.
They converted Bankside Power Station into Tate Modern and are responsible for the Beijing Olympics stadium.
The 23,000 square metres of space will include areas for contemporary art, several galleries and two performance zones.
The cost is expected to be comparable to Tate Modern's original construction bill.
Sir Nicholas said he had been working with about 20 other institutions close to the complex to develop the area around the South Bank as "London's cultural quarter".
Referring to the Olympics, he said he wanted "to do something which will take us forward and make this part of London the centre that can be regarded as a counterpart to what is happening in east London in 2012.
"I believe we will see an extraordinary explosion of activity in this area around Tate Modern, around South Bank, around all those extraordinary arts facilities that you see there," he added.
Tate director Sir Nicholas Serota is "confident" it will open in 2012
The London Development Agency - overseen by the capital's mayor Ken Livingstone - is to provide £7m towards the financing of the project.
And Sir Nicholas said the Tate was certain that it could find the funds required to complete the extension.
"We've done it before, and we're confident that if we can raise the money in good time, we have capacity also to deliver this building in 2012."