Laura Lezza / Getty Images The stricken Costa Concordia is prepared as the parbuckling project to upright the ship is set to begin on Sept. 15, 2013, near the Italian island of Giglio

It has been jutting out of the sea just off the Italian island Giglio for 20 months, but today the wreck of the Costa Concordia cruise liner will be raised to an upright position as part of the largest salvage operation ever conducted.

Workers have been waiting for favorable weather conditions in order to undertake the crucial rotation, known as parbuckling. If the vessel is not moved before winter sets in, the fear is that the already heavily corroded hulk will deteriorate to a state where it may break apart, releasing toxic substances into the sea.

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The Costa Concordia is twice the weight of the Titanic, and salvaging it is a mind-boggling operation that has already cost more than $800 million.

In order to carry out the parbuckling, a fake bottom has been built underneath the hull and 50 massive chains and winches have been attached to the vessel, as have huge tanks, or caissons, which will keep the ship afloat once upright. Once rotated, the ship will be moved to a mainland port, where it will be searched for missing bodies, and then scrapped. The parbuckling is the most sensitive stage of the salvage operation, and can be followed live here.

Just before 1 p.m. local time (7 a.m. Eastern), engineers announced that they have freed the ship from the reef and have successfully moved it onto the specially-constructed platforms underneath. No bodies were found in the process, leaving two missing people still unaccounted for.

[BBC]

This post has been updated.