LONDON — There is a monster beneath the streets of London, menacing the East End underworld.

What has been named the Whitechapel fatberg is a rock-solid agglomeration of fat, disposable wipes, diapers, condoms and tampons. It was discovered to the east of the city’s financial district, occupying a sixth of a mile of sewer under Whitechapel Road, between one of London’s largest mosques and a pub called the Blind Beggar, where walking tours are taken to reminisce about a notorious gangland murder.

Thames Water, the capital’s utility, said the fatberg weighed as much as 11 of the city’s double-decker buses: more than 140 tons. That is 10 times the size of a similar mass that the company found beneath Kingston, in South London, in 2013, and declared the biggest example in British history.

To prevent the contents of the sewer from flooding streets and homes nearby, the utility is sending an eight-member team to break up the fatberg with high-powered jet hoses and hand tools. The task is expected to take them three weeks, working seven days a week.

“It’s a total monster and taking a lot of manpower and machinery to remove,” said Thames Water’s head of waste networks, Matt Rimmer. “It’s basically like trying to break up concrete.”