A floating tank fastened to the Costa Concordia shipwreck to help lift the 114,500-ton vessel from the Giglio island seabed fell off on Tuesday.
The accident has caused a steel pontoon to tilt, possibly threatening the stability of the ship.
The tank was one of 19 watertight boxes which must be fixed onto the sides of the stricken ship to complete what is considered the largest re-float in history.
Photos:The Concordia: Recounting a Disaster
The tanks will be emptied of water and filled with air, providing buoyancy to raise the ship off the artificial seabed where it stands now, after it was set upright in September.
Sandwiched between the caissons, the cruise liner will be towed to a yet unnamed port for dismantling.
Engineers have so far installed three of the 19 tanks. The one which fell off was set up between April 26 and 28. It was already underwater when it collapsed in two phases.
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Titan-Micoperi, the consortium overseeing the operation, stated the problem was caused by a tangled chain.
"The situation is under control and our technicians will intervene as soon as possible to restore the tank's original balance," Giglio News reported the U.S.-Italian consortium as saying.
It will now be up to the Monitoring Observatory, which include third parties like the Italian civil protection body and the ministry of the environment, to decide how to continue the refloating project.
Photos: Concordia Pulled Upright
"The operations related to the Concordia dismantling must be carried safely and with the minimum impact on the environment," Gian Luca Galletti, the ministry of the environment, said.
About two-and-a-half times the size of the Titanic, the Concordia struck a rock off Giglio Island and capsized on Jan. 13, 2012, after captain Francesco Schettino, on trial for manslaughter, allegedly drove it on an unauthorized route too close to shore, ripping a huge gash in the hull.
The ship claimed 32 lives as it tumbled onto its side with more than 4,200 people aboard two years ago. Among the victims, Indian waiter Russel Rebello is still missing.
Image: The accident has caused a steel pontoon to tilt, possibly threatening the stability of the ship. Credit: Giglio News