Three people are confirmed dead after a cruise ship carrying more than 4,000 people ran aground off Italy.
There were scenes of panic as the Costa Concordia hit a sandbar on Friday evening near the island of Giglio and listed about 20 degrees.
Most people reached land by lifeboats but some swam to shore.
At least 50 people have not yet been accounted for, Italian officials say, but they caution that the passenger list may not be fully up to date.
Coast guard vessels are combing the waters around the ship, while divers are searching the submerged decks.
The regional prefect's office said 4,165 out of 4,234 people on board had been accounted for, the Italian news agency Ansa reported.
It is clearly an unexpected disastrous happening that should never happen. And this disaster is not in any way connected to waves,the sea was calm before, during, and after. Fortunately that uncomplicated the rescue efforts.
As the cause of the disaster is basically unknown at the moment, Sean Rayment of UK Telegraph reported this expert opinion according to Malcolm Latarche, the editor of the global shipping magazine IHS Fairplay Solutions:
. . . the ship was powered by a bank of six diesel-electric engines which effectively worked as an onboard power station designed to supply electricity to all parts of the vessel.
But like power stations on land, the engines are prone to electrical surges and troughs caused by “harmonic interference”.
Mr Latarche added: “From the reports I have seen it seems there was an explosion followed by a blackout, which could have been caused by a power surge. There are various back-up systems in place on all ships but they may have failed also."
Mr Latarche said it was possible the cruise ship experienced the same problem that saw the Queen Mary 2 (QM2) lose power in September 2010 as she was approaching Barcelona.
He continued: “Once you have a problem with the electric supply to the ship’s main propulsion motors that could lead to a problem with steering. Once you are in a position where you cannot control a ship's speed and direction you have a problem until you can get those systems back on line. It seems that this may have happened quite close to land, in shallow water. When you can’t steer you are going to run aground and hit rocks at some point.”
Once the ship had run aground on a sand bank, Mr Lartarche said, it was only a matter of time before it would begin to keel over.
He added: “A ship is designed to float in a certain depth of water. An ocean cruise ship is not designed to float in 20ft of water. It needs much more than that to remain upright. If it was in a dry dock it would be supported with blocks and supports to keep it upright. That situation doesn’t exist just off the coast. So unless the Costa Concordia was fortunate enough to be sitting on relatively flat ground, with very soft mud which would allow it to sink in and support the ship in some way, the vessel will have no alternative but to turn over on its side.
“If the captain had no steering or reduced steering it may have been that he had no choice where he was heading and that is why he ended up in shallow water but he also may have decided that he needed to head to safer waters so that he could use the lifeboats closer to land.
"This, afterall, was a passenger ship and there would have been lots of elderly and young people on board so evacuation in lifeboats is not ideal."
Mr Latarche's explanation of events fits in with comments made by Francesco Paolillo, a local coastguard commander, who said the accident occurred shortly after 10.30pm about three hours after the Concordia had begun its voyage from the port of Civitavecchia en route to its first port of call, Savona, in northwestern Italy.
So disasters can happen even without the encounter of freaque waves. Let's pray for the lost passengers and all of the ones onboard can be safely restoring their holiday venture.