Charles Saatchi is to open one of the world's largest private galleries of contemporary art and go into direct competition with Tate Modern.

The new gallery, in King Street, Chelsea, is replacing Saatchi's previous site at County Hall, which closed after the collector breached the terms of the lease.

The new location will feature 15 large rooms spread over three floors and cover 50,000sqft.

The Tate features a huge Turbine Hall and three floors of galleries that run the length of the 200 metre-long building, with a total of 371,350 square feet floor space.

Like the Tate, the Saatchi will be free to visitors when it opens in spring.

It will have longer opening hours than any other British gallery or museum, running from 10am to 10pm most days, thanks to sponsorship from New York-based auction firm Phillips de Pury, which is opening a British European HQ and auction rooms in Victoria later this month.

Saatchi, 64, is planning to launch his gallery with a show featuring his vast collection of contemporary Chinese art.

It will be followed by an exhibition by new US artists and then a show of contemporary Indian art.

The latest purchase by the collector, who has fostered the careers of Damien Hirst and Tracey Emin, is a painting of Nazi Holocaust mastermind Heinrich Himmler. Saatchi paid a reported £3,000 for the portrait by Jasper Joffe, 32.