Several people appear to have survived in an air pocket of a capsized South Korean ferry, the father of one of the school children aboard the boat told a Reuters reporter accompanying families out to the scene of the disaster on Thursday.
About 290 people are still missing out of 450 passengers on the Sewol ferry, which capsized in still-mysterious circumstances off the Korean peninsula on Wednesday in what could be the country's worst maritime accident in 20 years.
Many of the passengers were school children from one high school on the outskirts of Seoul.
"(The child) told me in the text message, 'I am alive, there are students alive, please save us quickly," the father said.
Coastguard and navy divers resumed searching on Thursday after the ferry capsized in sight of land on a trip from the port city of Incheon to the holiday island of Jeju, about 100 km (60 miles) south of the peninsula.
Grieving family members gathered early on Thursday on the quay of the coastal city of Jindo, huddled in blankets against the spring cold as efforts to find the missing went into a second day.
One parent, Park Yung-suk, told Reuters she had seen the body of her teenage daughter's teacher brought ashore earlier in the morning.
"If I could teach myself to dive, I would jump in the water and try to find my daughter," Park said as light rain fell.
So far 179 people have been rescued and six confirmed dead.
As coastguard officials arrived at Jindo on Thursday, waiting relatives jeered at them, shouting: "The weather's nice, why aren't you starting the rescue."
It is not known why the 6,586 tonne vessel, built in Japan 20 years ago, sank.
Nautical charts of the wider area show reefs and shallow waters, although one government official appeared to discount the possibility the ship had hit a rock.
It was not immediately clear why the Sewol ferry had listed heavily onto its side in apparently calm waters off South Korea's southwest coast, but some survivors spoke of a loud noise prior to the disaster.
There were reports of the ferry having veered off 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.
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, in a statement read out to local media, a company official 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 David Chance; Editing by Dean Yates)