Refugee advocates say the family camp for asylum seekers on Nauru was evacuated yesterday after an unexploded bomb was uncovered.
The Refugee Action Coalition says the exact nature of the uncovered ordnance was not known, but it was told it was a big one.
Nauru was occupied by the Japanese during the Second World War.
An unexploded Howitzer artillery shell was found in the family camp after heavy rain in April 2014.
The coalition says the latest discovery has renewed fears that the site of the family camp had not been properly assessed for unexploded ordnance.