The Rio Olympic Aquatic Centre had to be evacuated just 90 minutes before Australian swimmers were due to arrive after a suspicious package was found.
SBS News understands the package was possibly a piece of luggage or an unattended toolbox left behind in the centre.
The centre has since been reopened.
On Monday emergency services carried out a controlled explosion on a backpack outside the Maracana Stadium, where the opening ceremony will be held, as part of a training exercise.

