A huge 'sandcastle' has been built around a large unexploded WW2 bomb dredged up from a river ahead of it being detonated by army experts.

A wall of large sand-filled containers has been constructed around the rusty 250kg shell which was found during building work at a Great Yarmouth Quay, Norfolk.

Dozens of nearby residents have been evacuated and a no-fly zone put in place over the area.

The army descended on the scene in Great Yarmouth, Norfolk, yesterday (Feb 8) and a 400-metre cordon has been erected so a controlled explosion can take place by army disposal specialists.

The WWII bomb was found during dredging work in the River Yare on Tuesday (Feb 7).

The army will now cut into the bomb and carry out a controlled explosion. If successful, the rest of the device will be taken to sea for another controlled explosion.

However the police have since said there is now a risk of rupturing gas pipelines going into over 100 properties and businesses.

Superintendent Nathan Clarke of Norfolk Constabulary said: "It was all going to plan until about 9pm last night."

"Defences around the sandblast wall have been built and the Explosive Ordnance Disposal team should have started cutting the bomb. "

"However, with such an incident, calculations are absolutely necessary before each stage of the process."

Supt Clark said before cutting began the disposal team calculated the risk to infrastructure in the area.

It was discovered that gas pipes leading to more than 100 properties and businesses in the area were close to the confined blast area.

He added: "We cannot be confident the blast from a controlled explosion won't rupture the gas pipes."

"The process has since been halted. Currently, we are seeking scientific advice and running calculations about what our next steps may be."

"There is no quick solution. But ultimately, public safety is our top priority."

"We are getting the best advice possible and we will inform the public as soon as we know."

"The public has been exceptionally supportive throughout this process."

A major incident was declared on Tuesday night after the bomb was found by Bollard Quay.

Rest centres have opened in two locations and roads remain closed around the area.