LONDON -- British engineers say they have launched a "sewer war" against a giant fat blob clogging London's sewers.

A contractor employed by Thames Water to help break up a massive fatberg lodged in London's sewers is seen before descending underground to get to work, in a photo released by the utility company on Sept. 12, 2017. Thames Water

Thames Water officials said Tuesday it is likely to take three weeks to break up the outsize fatberg lodged about 4 yards under the streets of Whitechapel, in East London.

They caution against expecting quick results as the fatberg is 250 yards long and weighs as much as 11 double-decker busses -- or about 143 tons.

The unsavory blob consists of congealed wet wipes, diapers, condoms and discarded fats and cooking oil.

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Thames Water's Matt Rimmer says the fatberg is "up there with the biggest we've ever seen. It's a total monster and taking a lot of manpower and machinery to remove as it's set hard."

He said the task is "basically like trying to break up concrete."

Eight workers are using high powered jet hoses to break up the blob before sucking it out into tankers for disposal at a recycling site.

This isn't London's first battle with a fatberg, but it may be the biggest enemy Thames Water has ever faced.

In 2013, workers broke up a fatberg they described as the largest ever encountered. That one, found in the sewers under the ritzy southwest London suburb of Kingston, weighed in at a mere 15 tons and was only as long as a single bus.