Rome, Italy -- The Italian captain of the cruise ship that ran aground -- killing three people and injuring 20 more -- was arrested late Saturday and is being investigated for abandoning ship and manslaughter, said a local prosecutor in Grosetto, Italy.
Abandoning ship is the more serious of the potential charges, authorities said.
The captain, Francesco Schettino, had been earlier interviewed by investigators in Porto Santo Stefano about what happened when the 4,200-passenger Costa Concordia struck rocks in shallow water off Italy's western coast, said officer Emilio Del Santo of the Coastal Authorities of Livorno.
Authorities were looking at why the ship didn't hail a mayday during the accident near the Italian island of Giglio on Friday night, officials said. The ship is owned by Genoa-based Costa Cruises.
"At the moment we can't exclude that the ship had some kind of technical problem, and for this reason moved towards the coast in order to save the passengers, the crew and the ship. But they didn't send a mayday. The ship got in contact with us once the evacuation procedures were already ongoing," Del Santo said prior to the announcement of the arrest.
Giuseppe Orsina, a spokesman with the local civil protection agency, said 43 to 51 people were missing, though authorities are reviewing passenger lists to confirm the exact figure.
"These people could be still on the island of Giglio, in private houses or in hospitals," Orsina said.
The coast guard said 50 to 70 people could be missing.
Authorities said earlier Saturday they believed everyone was accounted for, but that they did not have a definitive list of names.
"Fear and panic are comprehensible in a ship long over 300 meters with over 4,000 passengers," Del Santo said. "We can confirm that the ship has a breach on the hull of about 90 meters, and that the right side of it is completely under water."
Two French tourists and a crew member from Peru were killed, Port authorities in Livorno said. One of the victims was a 65-year-old woman who died of a heart attack, according to authorities.
A surviving crew member, Rosalyn Rincon, 30, of Blackpool, England, said she wanted to know why the cruise ship was sailing so close to shore. She described a harrowing grounding of the vessel, whose tilting and rising water evoked the film "Titanic," she said.
"I'm pretty much angry, and I want to know why we were so close to the coast," said Rincon, who works as a dancer on the ship and was entertaining passengers by performing a trick inside a box with a magician when the accident occurred.
Nautilus International, a maritime employees trade union, called the accident a "wake-up call" to regulators.
"Nautilus is concerned about the rapid recent increases in the size of passenger ships -- with the average tonnage doubling over the past decade," said Nautilus general secretary Mark Dickinson in a statement. "Many ships are now effectively small towns at sea, and the sheer number of people onboard raises serious questions about evacuation."
The ship was 2.5 miles off route when it struck a rocky sandbar, according to the Italian Coast Guard. Local fishermen say the island coast of Giglio is known for its rocky sea floor.
Gianni Onorato, president of Costa Cruises, expressed "deep sorrow for this terrible tragedy," but said the cruise line was unable to answer all the questions that authorities are now investigating.
"On the basis of the initial evidence - still preliminary - Costa Concordia, under the command of Master Francesco Schettino, was sailing its regularly scheduled itinerary from Civitavecchia to Savona, Italy, when the ship struck a submerged rock," Onorato said in a statement before the announcement of the captain's announcement.
"Captain Schettino, who was on the bridge at the time, immediately understood the severity of the situation and performed a maneuver intended to protect both guests and crew, and initiated security procedures to prepare for an eventual ship evacuation," he continued.
"Unfortunately, that operation was complicated by a sudden tilting of the ship that made disembarkation difficult," Onorato said.
Some passengers fell into the chilly waters during the rescue, Italy's ANSA news agency reported.
The huge ship, which was lying on its side in shallow water Saturday evening, was carrying about 3,200 passengers and 1,000 crew members when it ran aground around dinner time.
Initial reports suggested as many as six people had been killed, but it was unclear why the number dropped. About 1,500 of the people aboard the ship were on their way home Saturday, the Civil Protection Authority said.
Passengers described how the lights went out and it then became clear the ship had hit something, prompting scenes of chaos.
Laurie Willits from Ontario, who was watching a magic show with her husband at that moment, told CNN: "We heard a scraping noise to the left of the ship and then my husband said 'we're sliding off our seats.'"
The couple ran to their cabin to get coats and life jackets before making their way to a lifeboat. Emergency instructions in English were hard to hear, Willits said.
Panic spread as people scrambled to find lifeboats in the dark as the ship quickly leaned to one side. Access to some lifeboats was hampered by the ship's tilt into the water, adding to the confusion.
Willits and her husband, who managed to get into a lifeboat about an hour to 90 minutes after the alarm was raised, watched from a pier on the island as the ship slowly sank until it was at an almost 90 degree angle in the water.
"I'm exhausted, I haven't had any sleep, I'm hungry," Willits said, but added that she was relieved to have been able to call her family thanks to the help of people on the island.
The coast guard said three helicopters were used to rescue some passengers from the ship.
Adm. Ilarione Dell'Anna, head of coastal authorities for the port city of Livorno, said an investigation is under way.
"There has probably been a technical blackout," he said. "The ship was dangerously near the coast. We worked all night in a state of maximum emergency.
"Fortunately the sea conditions have helped us, otherwise -- given the high number of people to rescue, 4,231 -- we could have had a completely different scenario: a real tragedy."
Many of those rescued in the early hours were taken to small churches and other buildings around the island for shelter. Some were still wearing the pajamas and slippers they had on as the ship went down, as they waited for help Saturday morning at reception centers set up on the island.
Costa said it was focusing on the final stages of the emergency operation and helping passengers and crew return home.
"It is a tragedy that deeply affects our company. Our first thoughts go to the victims and we would like to express our condolences and our closeness to their families and friends," Costa said on its website.
The Concordia, built in 2006, was on a Mediterranean cruise from Rome with stops in Savona, Marseille, Barcelona, Palma de Mallorca, Cagliari and Palermo, according to the cruise line. It was unclear how far into the cruise the grounding occurred.
Most of the passengers on board were Italian, as well as some French and German citizens. CNN affiliate America Noticias, in Peru, said a group of 32 Peruvians were also onboard. Brazil's state-run Agencia Brasil said 53 Brazilians were on the cruise ship: 47 passengers and six crew members, according to the foreign ministry. An estimated 126 Americans were also on board, according to the U.S. State Department. There were no reports of injured Americans.
The United Kingdom's Foreign and Commonwealth Office was working with Italian authorities to identify British nationals on the cruise, a spokesman said.
Another Costa ship was involved in a deadly 2010 accident when the Costa Europa crashed into a pier in Egypt's Sharm el-Sheikh during stormy weather, killing three crew members.