LONDON - A fatberg weighing more than 300 tons is clogging the sewer system, expected to be stuck in place for weeks.

The fatberg, a mass of waste and products that aren't supposed to be flushed, is thought to be more than half a mile long.

Severn Trent Water, the water management company dealing with the clog, said it might be one of the biggest blockages they've ever dealt with.

The company was alerted to the problem through a sewage sensor, which monitors water levels.

Residents are advised to stop flushing cooking fat, wipes, diapers and other materials.