About 60 people are spending the night away from home after a suspected Second World War bomb was discovered containing up to 1,000lb (450kg) of explosives.
The unexploded device led to the closure of the A259 South Coast Road when it was found shortly before 3pm on Wednesday in Peacehaven, Sussex. A 200-metre cordon was also set up.
Temporary accommodation was provided for those who were forced to leave their homes, with Sussex Police saying dozens of people were being housed in rest centres in the town.
Chief Superintendent Nick May, of Sussex Police, said: "We recognise that it has meant considerable upset for residents - including children and senior citizens - who have had to abandon their homes at short notice, and for motorists faced with delays and diversions to their journeys."
Emergency services and experts from explosive ordnance disposal are working at the site, police added.