* Poor weather conditions may hamper effort
* Mystery surrounds capsize of ship
* Nearly 280 people still missing, many of them teenagers
By Narae Kim
JINDO, South Korea, April 17 (Reuters) - South Korean coastguards and navy divers resumed their search on Thursday for nearly 280 people still missing after a ferry capsized in what could be the country's worst maritime disaster in over 20 years.
They will also be seeking answers to many unanswered questions surrounding Wednesday's accident, notably what caused the Sewol vessel to list and then flip over entirely, leaving only a small section of its hull above water.
Rescue efforts on Thursday could be be hampered by difficult weather conditions, however, amid forecasts of rain, strong winds and fog.
Of 462 passengers on board the ferry when it set sail from the port of Incheon late on Tuesday, 179 have been rescued and six people are known to have died.
Nearly 340 of the passengers were teenagers and teachers from the same school near the capital Seoul on a field trip to Jeju island, about 100 km (60 miles) south of the Korean peninsula.
Parents of missing children faced an agonising wait for news as they gathered in Jindo, a town close to where ferry capsized.
"My tears have dried up," said one mother, who did not give her name. "I am holding on to hope. I hope the government does everything to bring these kids back to their mothers."
At the dockside in Jindo, women sat and stared out at the black, calm sea before them, quietly sobbing.
It was not immediately clear why the Sewol ferry had listed heavily on to its side and capsized in apparently calm waters off South Korea's southwest coast, but some survivors spoke of a loud noise prior to the disaster.
A member of the crew of a local government ship involved in the rescue, who said he had spoken to members of the sunken ferry's crew, described the area as free of reefs or rocks and said the cause was likely to be some sort of malfunction on the vessel.
There were reports of the ferry having veered off its course, but coordinates of the site of the accident provided by port authorities indicated it was not far off the regular shipping lane.
The ferry sent a distress signal early on Wednesday, the coastguard said, triggering a rescue operation that involved almost 100 coastguard and navy vessels and fishing boats, as well as 18 helicopters.
A U.S. navy ship was at the scene to help, the U.S. Seventh Fleet said, adding it was ready to offer more assistance.
According to a coastguard official in Jindo, the waters where the ferry capsized have some of the strongest tides of any off South Korea's coast, meaning divers were prevented from entering the mostly submerged ship for several hours.
Adding to the sense of confusion on Wednesday, the Ministry of Security and Public Administration initially reported that 368 people had been rescued and that about 100 were missing.
But it later described those figures as a miscalculation, turning what had at first appeared to be a largely successful rescue operation into potentially a major disaster.
The ship has a capacity of about 900 people, an overall length of 146 metres (480 feet) and weighs 6,586 gross tonnes. Shipping records show it was built in Japan in 1994.
According to public shipping databases, the registered owner of the ship is Chonghaejin Marine Co Ltd, based in Incheon. Reuters was unable to reach the company by phone.
Earlier, company officials offered an apology over the accident but declined to comment further.
The databases showed that Chonghaejin Marine Co Ltd became the owner of the vessel in October, 2012. (Additional reporting by Jack Kim, Ju-Min Park, Choonsik Yoo, Meeyoung Cho and James Pearson in SEOUL and Jonathan Saul in LONDON; Writing by Mike Collett-White; Editing by Andrew Roche)