Rescue workers have suspended their search of the Costa Concordia after the cruise ship moved, making it too risky for divers to operate, the Italian Coast Guard said Friday.
Sensors on board the vessel measured movement, Massimo Maccheroni, of the Coast Guard general command, told CNN.
"When this happens all rescue forces have to leave the ship, (so as) not to put their lives in danger," he said.
The authorities are now assessing their options. One possibility being considered is an attempt to anchor the vessel to the rocks off Giglio island using chains.
But, warned Maccheroni, "It's very difficult. The Concordia weighs 110,000 tons and it's like a 300 meter-high skyscraper in an horizontal position."
Italian authorities are considering when to call off the search for survivors and start the recovery operation, which would mean salvage workers can start emptying the ship's huge fuel tanks.
At least 11 people are known to have died in the disaster, and 21 are still missing, according to the Italian Crisis Unit.
A week after the ship ran aground off the Tuscan coast