A MASSIVE crack in a concrete floor – said to symbolise racism and the gulf between white Europeans and the rest of humanity – has been unveiled as the central exhibit at London's Tate Modern gallery.

Shibboleth, by Colombian sculptor Doris Salcedo, runs the full 167-metre length of the massive Turbine Hall at the famous gallery on the south bank of the River Thames.

It starts as a hairline crack then widens and deepens as it zig-zags across the room. Salcedo told reporters it took more than one year to make and she spent the last five weeks installing it.

Gallery: Tate Modern shows off big crack »

"What is important is the meaning of the piece. The making of it is not important," she added.

Asked how deep the fissure goes, she replied: "It's bottomless. It's as deep as humanity."

Wire mesh embedded within the exposed opening was used because it is "the most common means of control used to define borders and divisions," the artist said.

"It represents borders, the experience of immigrants, the experience of segregation, the experience of racial hatred. It is the experience of a Third World person coming into the heart of Europe.

"For example, the space which illegal immigrants occupy is a negative space. And so this piece is a negative space."

Shibboleth is Salcedo's first public commission in Britain and the eighth in the Unilever Series of works occupying the Turbine Hall at the former power station. The last was Carsten Hoeller's hugely popular giant slides.

Tate Modern staff will be stationed near the crack to warn visitors about the dangers of tripping and falling into the void.

The installation will be removed April 2008 by filling in the crack. Tate director Nicholas Serota said the "scar" would remain "as a memory of the work and also be a memorial to the issues Doris touches on."

Shibboleth comes from the Hebrew used in the Old Testament to mean a custom or practice that distinguishes someone as an outsider.