MOKPO/SEOUL (REUTERS) - The first alarm from a sinking South Korean ferry was raised in a phone call from a child on board to a fire station at 8.52am on the morning the boat capsized, three minutes after the vessel made its fateful last turn.

That call was forwarded to the coastguard two minutes later and was followed by about 20 others to the fire brigade, a fire station officer told Reuters.

The first call as the ferry began sinking on Wednesday was from a boy whose voice was shaking and sounded urgent, a fire officer told MBC TV. It took a while to identify the ship as the Sewol because he was flustered.

The fire station official asked him to switch the phone to the captain, and the boy replied: "Do you mean teacher?" The pronunciation of the words for "captain" and "teacher" is similar in Korean.

The South Korean government released a timeline of the ferry's last minutes while it was still stable and afloat.

The Sewol made its scheduled turn en route to the holiday island of Jeju off the southern tip of the Korean peninsula at 8.49am and started listing within a minute. By 8.55am it was drifting back on itself and heeling to port.

The Sewol was on a routine trip south from the port of Incheon to sub-tropical Jeju.

Of the 476 passengers and crew on board, 339 were children and teachers on a high school outing. Only 174 people have been rescued and the remainder are all presumed to have drowned.