The captain of a river cruise ship that collided with a smaller sightseeing vessel has been charged over the accident in Budapest that killed seven South Korean tourists and left 21 missing.

A Budapest court official said the Ukrainian captain of the Viking Sigyn had been charged, but gave no further details.

The 64-year-old was detained on Thursday for questioning a day after his vessel collided with the smaller Mermaid, carrying mainly South Korean tourists, causing it to overturn and sink on a busy stretch of the Danube.

He was questioned for "endangering waterborne traffic resulting in multiple deaths", police said at the time.

The captain's lawyer, Balazs Toth, said the court had granted bail, but prosecutors were appealing it so his client remained detained.

"My client has not changed his statement made as a witness. He insists that he has not made any error," his other lawyer, Gabor Elo, told reporters after the hearing.

Strong currents have hampered the search for those missing - 19 South Koreans, the second boat's Hungarian captain and one crew member, preventing divers from reaching the submerged boat.

A Hungarian police spokesman said today that seven of the South Korean victims have been identified but their names have not been released.

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Near the accident site, a floating crane has been erected, as well as a small pier for use by divers.

But with the Danube swollen after weeks of rain, the strong current has complicated plans to lift the wreck, and the prospects of finding any more survivors are seen as very slim.

Serbia, Romania and Croatia - countries along the Danube, south of Hungary - have also been asked to help in the search after South Korean Foreign Minister Kang Kyung-wha insisted in Budapest on Friday that her country would not give up hope of finding survivors.

One of the bodies was found around 11km downstream of the accident site.

People have been laying flowers along the river bank and on a bridge above the spot where the collision took place, as well as at the South Korean embassy.

Today, black flags were flying along the bridge.

The collision happened on a popular part of the river, from where sightseers can view the city and parliament, which is lit up at night.

Larger river cruise boats travelling on the Danube between Germany and the Black Sea typically spend several days moored in the capital.