The Tate Modern museum in central London has been transformed by graffiti artists from around the world.

The riverside facade of the world's most popular modern art gallery has been covered in giant murals by six urban artists.

They include Blu from Bologna in Italy, the artist collective Faile from New York, and Sixeart from Barcelona.

It is the first display of street art at a major museum and a further sign that graffiti is taken seriously by critics and collectors.

Original work by street artists now sell for hundreds of thousands of pounds at auction and online.

Last month, the elusive urban artist Banksy organised a festival of graffiti and covered a whole street near Waterloo Station in original art.

He worked with 40 artists, including Faile, to create a huge display of stencil art which is expected to remain in the tunnel for at least the short term.

Banksy may well approve of the Tate transformation.

He wrote that graffiti "doesn't spoil buildings, in fact it's the only way to improve them".

The Tate is also offering a 'Street Art Walking Tour' of London and an interactive evening with experimental New York artists Graffiti Research Lab, using graffiti light projections to 'reface' the Tate.