(CNN) -- The effort to find nearly 280 people who remain missing in South Korea's ferry disaster is now in its third day. The Sewol suddenly started listing, took on water and capsized over a two-hour period Wednesday. Here's what you need to know to get caught up:
At least some people could still be alive
No one knows what has happened to the 276 people -- many of them Seoul high school students -- believed to be trapped in the ship. But rescuers are operating on the assumption that air bubbles inside the capsized ferry's hull could be sustaining them. Rescuers will work around the clock in a bid to find survivors, Yellow Sea Maritime Police Chief Kim Soo Hyeon told reporters Thursday. So far, 25 people are known to be dead, according to the South Korean Coast Guard. Another 179 have been rescued, authorities said.
But poor conditions are hindering the rescue effort
The cold, murky water at the scene is making it difficult for divers to find a way into the ship. About 512 divers working in 12-hour shifts are involved in the operation, Kim said. But they've so far been unable to get into the ship and find a way to pump air into the hull, which could help raise the ship and extend survival time for anyone inside. Sea cranes that could help lift and move the ship are on the way and should arrive Friday, authorities said.
Questions have come up about how many lifeboats deployed
Social media video acquired by CNN affiliate JTBC showed at least 12 of the white survival capsules still attached to the ferry even as it was keeled over in the water. It was unclear, however, exactly how many lifeboats had deployed. Initial reports from YTN said it was one, but the JTBC video shows what appears to be two lifeboats next to the ship. CNN has not been able to independently confirm the reports, which Kim said authorities are investigating.
Possible causes for the incident begin to come into focus
It appears highly probable that the Sewol deviated from its planned course, causing the accident, Kim said. But, he said, it did not appear to hit a rock. He did not offer an explanation for what had happened. South Korean media reported Thursday that investigators are looking into the possibility that the ship may have made an unusually sharp turn, shifting cargo on board and causing the ferry to tip onto its side and begin taking on water. CNN has not confirmed those reports.
And the ship's captain and owner have apologized
Ferry captain Lee Joon Suk tearfully apologized to reporters at a South Korean Coast Guard office where he was being questioned. "I am sorry, I am at a loss for words," he said. A spokesman for the ship's operator, Chonghaejin Marine Corp., also apologized, saying the company "will do our best not to lose any more lives."