Vandals drove a crane into the River Liffey last night, a spokeswoman for Dublin Corporation said. A rescue operation is now under way to save the vehicle before the river reaches high tide.
Gardaí have sealed off the south quays, causing severe traffic disruption in the city centre.
The crane was being used on refurbishment work on the landmark Ha'penny bridge. The temporary bridge in place, while this work is ongoing, has been shut for the duration of the salvage operation.
The spokeswoman said vandals mounted a floating pontoon, broke into the cab of the crane and drove the it into the water.
She could not confirm the value of the crane or how much damage it had suffered.
A Garda spokeswoman said detectives from Pearse St Garda station were investigating the incident. However she said an accident has not been ruled out as a cause.