The emergency services have declared a major incident, after the discovery of an unexploded Second World War bomb at the site of Great Yarmouth's third crossing project.
Army specialists were at the scene late into the night, while a 400 metre cordon remained in place.
Several roads have been closed and rest centres have been established in the town, to accomodate those told to leave their homes.
Officials said the disruption was likely to last into morning, with the cordon expected to remain in place for another 24 hours, as experts try to make the device safe.
Chief Inspector Matt Dyson, from Norfolk police, said: “Our priority will always be the safety of the public and we’re working alongside our partners and taking advice from army experts around cordons while work continues to safely resolve the incident.
“We appreciate the measures put in place for people’s safety will cause some disruption however public safety is paramount and we would advise people these restrictions will be in place overnight and into tomorrow.
“Rest centres have been opened and officers along with staff from the borough council are visiting homes to check and identify any vulnerable people who need assistance.
READ MORE: Live updates as suspected unexploded bomb discovered in Great Yarmouth
The drama began at 11.36am on Tuesday (February 7) when officers were called by a contractor working at the development site of the third river crossing who reported finding what they believed to be an unexploded device.
It was discovered during dredging work in the River Yare at Bollard Quay close to the junction with Boundary Road.
A 400m cordon was set up affecting hundreds of households and businesses.
People who are asked to evacuate are strongly advised to do so and those who are unable to seek refuge with friends and family can go to one of the two rest centres.
They are asked not to return to their homes until they are told it is safe to do so.
The rest centres are at St Georges Theatre in King Street, Great Yarmouth, and Mesh - Shrublands Youth and Adult Centre in Magdalen Way, Gorleston.
Refreshments and bedding are available.
Fire officers are also assisting police with the evacuation.
Road closures are likely to remain in place for some time.
Southtown Road is closed from its junction with Tollgate Road all the way to Beccles Road.
Williams Adam Way, off Southtown Road and Tollgate Road, off Southtown Road, are also closed.
Litchfield Road, off Southtown Road, and Boundary Road, off Southtown Road are partially closed.
Officers are asking pedestrians and motorists to avoid the area.
The Explosion Ordnance Device team is at the scene.
An emergency helpline has been set-up for people who require assistance with evacuation from the exclusion zone. This helpline is 01493 330369 and should not be used for general advice.
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