A large chunk of wall which lines the river in Norwich close to the city centre has collapsed into the water.

Eastern Daily Press: A 20ft section of wall on the River Wensum by New Mills Yard has fallen into the river. Picture: ArchantA 20ft section of wall on the River Wensum by New Mills Yard has fallen into the river. Picture: Archant (Image: Archant)

The piece of boundary wall, measuring around 15ft high and 20ft wide, slipped into the River Wensum on Monday near New Mills Yard, disappearing beneath large overgrowth in the water.

The Environment Agency said it did not pose any risks although did not state what may have caused the brick wall to give way.

The wall is located at the rear of the old BT telephone exchange site in Westwick Street, which was being used to store building materials for development works taking place in St Duke Street.

The missing wall was first noticed on Tuesday by Ken Hurst, 72, of The Moorings, who was standing at his balcony facing the river when he spotted the gaping hole in the wall.

Eastern Daily Press: Ken Hurst, 72, noticed a large section of the wall on the River Wensum by New Mills Yard had collapsed into the river. Picture: Neil DidsburyKen Hurst, 72, noticed a large section of the wall on the River Wensum by New Mills Yard had collapsed into the river. Picture: Neil Didsbury (Image: Archant)

"It was a surprise to see the wall had been there one day and then the next day it wasn't," he said. "Nobody seems to be bothered but it isn't really visible to the public, I just so happen to live directly opposite it."

The former telephone network building, now owned by London-based developer Telereal Trillium, is also earmarked for redevelopment, with plans to convert it into 42 flats.

Mr Hurst said in February piles of building material, some stacked against the wall, started to appear in the area behind the telephone exchange building.

"Then these whopping big skips were placed there for building waste," he said. "There was constant movement of skip lorries."

Eastern Daily Press: A 20ft section of wall on the River Wensum by New Mills Yard has fallen into the river. Picture: ArchantA 20ft section of wall on the River Wensum by New Mills Yard has fallen into the river. Picture: Archant (Image: Archant)

He said earlier this month, the skips and material were taken away by lorries and a forklift and never seen again.

Mr Hurst contacted Norwich City Council to query whether the building works had begun at the telephone exchange but was told this was not the case.

In a letter to Mr Hurst, the council said the site was being used temporarily "in connection with the development of the old garage site on Duke Street."

A spokesman from the Environment Agency said an inspection was made at the site to assess the damage but that the flood defence wall was not affected.

Eastern Daily Press: Former BT Exchange, Westwick House, Westwick Street.Picture: ANTONY KELLYFormer BT Exchange, Westwick House, Westwick Street.Picture: ANTONY KELLY (Image: Archant Norfolk 2015)

She added: "We are satisfied that the debris from the structure is not posing any flood risk."

Telereal Trillium has been approached for comment.

Eastern Daily Press: A 20ft section of wall on the River Wensum by New Mills Yard has fallen into the river. Picture: ArchantA 20ft section of wall on the River Wensum by New Mills Yard has fallen into the river. Picture: Archant (Image: Archant)