Legendary Welsh singer Tom Jones shocked passers-by in central London on Wednesday by performing an impromptu set on a pavement to raise money for a cancer charity.

The 68-year-old thrilled hundreds of people who thronged around him snapping photographs on their mobile phone cameras, as he sang with only an acoustic guitarist alongside him.

As he belted out `It`s Not Unusual`, female members of the crowd began backup singing, prompting Jones to laugh mid-performance, while one man climbed up a tree to get a better look at the music superstar.

`We just happened to be walking past and I heard this singing, and I thought it sounded like Tom Jones,` said June, who was with her husband Nigel, as Jones sang in front of the Royal Festival Hall on the south bank of the River Thames in central London.

`He came across as very nice -- not at all flash.`

At the end of the performance, Jones told the crowd they had donated around 500 pounds (750 dollars, 600 euros), thanked them and was whisked away by security guards.

Jones performed four songs as part of the BBC`s Culture Show as part of their British Busking Challenge, where stars perform in a public place for charity.