The South Korean coastguard says it’s possible that some people could still be alive trapped in air-pockets inside the ferry

Bad weather on Thursday hampered the search and rescue efforts for any survivors of the South Korean ferry "Sewol" that sank in the sea off Jindo on April 17th.

Hundreds of people including many high school teenagers are missing after the ship capsized about 12 miles off South Korea's southwestern coast.

President Barack Obama Thursday expressed condolences to the families of the victims of the ferry sinking. He said the US will provide the South Korea with any help it needs to carry out rescue operations.

"South Korea is one of our closest allies, and American Navy personnel and US Marines are already on the scene assisting with the search and rescue efforts," Obama said. "I've directed our military to provide any and all assistance requested by our Korean partners in the days ahead."   

Obama is planning to visit Korea next week as part of a four-country tour of Asia.

"As I will underscore on my visit to Seoul next week, America's commitment to our ally South Korea is unwavering – in good times and in bad."

Among the ship's passengers were 340 children and teachers from the Danwon High School in Ansan, a suburb of the capital, Seoul.

South Korean journalist June Chang says hundreds of high school students and neighbors came to the high school Thursday to talk, to pray, to holding a candlelight vigil.

"There are students ranging from 9th grade to 12th grade all praying for their fellow students. Right now there's a candlelight vigil going on. All the students have pieces of paper with messages scribbled on them saying 'Stay strong,' 'Come back home safely,’ ‘Aren't you hungry? Come back so we can have a meal together.'"

Chang says the Korean Red Cross is on hand at Danwon High School providing food, blankets and counselling for anyone who needs it.

As for the ferry its now submerged 12 miles off the coast of South Korea. The ferry was carrying passengers to the island of Jeju. There was a total of 475 people including the crew on board.

The trip would normally take more than 13 hours. Investigators say it appears there was a dense fog that delayed the trip two hours.

"Unfortunately because there was a delay, there's speculation that the captain decided to take a shortcut for the journey so this is possibly why the ship might have hit an underwater rock or reef, which could explain why passengers felt an impact, a jolt, and they could hear a loud bang."

The picture of what happened next is still emerging based on survivor's accounts.

"Passengers were saying 'what do we do?' and some people were just trying to follow orders, because instructions were broadcast numerous times to stay put," Chang says. "The captain (Lee Joon-Seok) told the crew to evacuate (according to student interviewed by a local Korean TV station) so they just followed the captain's orders without saving anyone. So apparently that's their excuse. As to whether it’s true or not, I'm not sure, that's what's going around. For instance the life boats for this ferry were not released. They did not deploy any of them which is why there's a swirl of controversy at the moment."

Chang says there are ongoing search and rescue operations, and there's still hope for survivors.  Divers are pumping oxygen into the submerged ferry in the event that any passengers are trapped inside the vessel in air pockets.

The overnight water temperatures are cold enough to induce hypothermia in victims still in the water. In addition, strong currents and murky water is making it very difficult for divers to carry out the search.

As South Korean ferry came to a shuddering halt and was listing further and further into the water, some students on board sent harrowing text messages to their loved ones on shore.

A student texted his mother in Korean, "Mum, this might be the last chance to tell you I love you." His mother texted back, "why's that?" and then "I love you anyway."

That young man was one of the lucky who was rescued. In another text sent as the ferry was listing further and further into the water, a student wrote to her father.

Student: "Dad, don't worry. I'm wearing a life vest and am with other girls. We're inside the ship, still in the hallway."

Father: "I know that the rescue is under way, but shouldn't you be waiting outside the rail? Try to get out if you can."

Student: "The ship is too tilted. The hallway is crowded with so many people."

That young woman has yet to be located. 

Chang says it’s unfortunate that the students were about to embark on a four-day trip to Jeju Island. "It was something they were looking forward to so right now everyone's in shock and disbelief. We're all on the edge of our seats trying to find news of any survivors."