Google MapsHomes are to be evacuated after a suspected World War Two bomb was discovered at a building site in Newtownards.
Cllr Pete Wray said he understood 450 households were affected by Friday’s find at the Rivenwood housing development in Movilla Road.
The BBC has seen a notice that is being distributed which says homes and businesses within a 400m (0.25 miles) radius of the “sizeable” munition are to be evacuated by 10:00 BST on Sunday.
The notice also says the operation could take “five or more days to complete”.
OtherThe Ards Blair Mayne leisure centre is being set up as an “emergency support centre” for affected residents and it will be open from 09:00 BST.
The Ulster Unionist councillor told BBC News NI: “This is a very complex and unusual thing to happen.
“It was explained to me that this is only the second of this scale in the UK. Something similar happened in Plymouth.”
Earlier this year, a 500kg (1,102lb) German World War Two bomb forced the evacuation of thousands of people in Plymouth.