A 10-tonne lump of wet wipes and fat has been removed from a sewer in Chelsea, west London.

The toxic lump of congealed fat and household waste -- known as a fatberg -- was 40 metres long and so heavy that it broke the 1940s-era sewer.

Repairing the damaged sewer is expected to cost Thames Water £400,000 and take more than two months, the company said.

Stephen Hunt, a repair and maintenance supervisor at Thames Water, who is overseeing the fatberg's removal, said its size was staggering.

"We see blockages all the time on household sewer pipes, which are about big enough for a cricket ball to pass through, but to have this much damage on a sewer almost a metre in diameter is mind-boggling.

"The original sewer has been so badly abused by fat being chucked down the plughole we've had to opt for the time-consuming and disruptive option of replacing many metres of pipe."