South Korean coast guard officers say they did not have the right training or equipment to rescue passengers from the stricken ferry, Sewol.
The officers were speaking at the trial of the ship's crew members.
More than 300 passengers, most of them school children, died when the Sewol sank in April, in South Korea's worst maritime disaster in decades.
The accident sparked outrage, with the government and the ferry's crew and owners facing the fiercest criticism.
The captain and 14 crew members are on trial for a range of charges relating to the disaster. The captain and three others are accused of the most serious crimes, of negligent homicide.
Defence lawyers for the captain have in turn accused the coast guard of failing in their duty to rescue passengers.
In court on Tuesday in the southern city of Gwangju, the coast guard officers spoke for the first time of what they encountered when they reached the ship.
They said they had expected to find passengers waiting on the deck, and were unaware that many were still trapped inside cabins that were filling up with water.
An officer said he was ready to pull people from the water, but did not have the equipment or the training to go inside the sinking ship.
The officer also said he did not know Captain Lee Joon-seok was one of the first people he had rescued from the boat.
According to Rupert Wingfield-Hayes, the BBC's correspondent in Gwangju, one of the most damning pieces of evidence against the captain is a coast guard video that shows him fleeing the ship while hundreds of passengers remain stuck inside.
Last month, an interim report by the South Korean government said the authorities' negligence and corruption were partly responsible for the sinking of the ferry.
Investigators say the ferry had been illegally modified to carry more passengers and cargo, and was overloaded.
But prosecutors say the actions of the captain and crew - including instructing passengers to stay in their cabins as the ship listed - led to more deaths.
The head of the ferry operator and other company officials are facing a separate trial.
The company's billionaire owner, Yoo Byung-eun, went missing after the disaster and was found dead in June.
South Korea's Yonhap news agency reported on Tuesday that prosecutors had decided not to indict him.
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