BUDAPEST — Prime Minister Viktor Orban of Hungary on Friday promised a thorough investigation into the boat accident on the Danube river Wednesday night that left at least seven people dead in Budapest.
“We want to know precisely what happened and why it happened,” Mr. Orban told Kossuth, the state radio station, adding that the authorities would reveal their findings in due course.
Search and rescue operations continued around Margaret Bridge, one of a dozen that span wide sections of the Danube, which cuts through the heart of Budapest. It was near the bridge that the Mermaid, a sightseeing boat, was apparently clipped by the Viking Sigyn, a Swiss-operated river cruise ship, in heavy rain on Wednesday night.
Austrian and South Korean military rescue teams arrived in Budapest on Thursday and Friday to contribute to the search effort, but they were hampered by the rapid currents of the flooded Danube. One diver told the Hungarian daily Magyar Nemzet that the current was so strong that he was afraid to let go of a ladder he used in a test dive, for fear that he would be swept away.
According to vesselfinder.com, a boat-tracking website, the Viking Sigyn, which sustained minor damage in the collision, had left Budapest by Friday morning. Its last reported position was north of Budapest, heading to Passau in Germany. The head office of Viking River Cruises in Basel, Switzerland, did not immediately respond to a request for comment.
The Danube was expected to reach a high-water mark near Budapest on Friday, making the work of divers even more dangerous.
In addition to those killed, 21 people were listed by authorities as missing, but officials had little hope of finding survivors.
Officials have extended the search area downstream as far south as Serbia, Hungary’s neighbor on the river, Peter Szijjarto, Hungary’s foreign minister, said at a news conference on Friday.
The Danube was flowing at more than nine miles per hour, he said. A map on the police website showed that one body had been recovered about 15 miles downstream.
Preparations were being made to raise the capsized boat, Mr. Szijjarto said. “The goal is to retrieve the wreck as soon as possible and to recover the remains of those trapped inside,” he said.
“Those taking part in the rescue and recovery work are fighting against very difficult and dangerous conditions,” he said.
“It is impossible to get close to the wreck,” he added, noting that visibility was essentially zero and the ship was around 20 feet underwater.
The Hungarian authorities are investigating the crash as a possible criminal matter. The captain of the Viking Sigyn, identified only as Yuri C., a 64-year-old from Odessa, Ukraine, was taken into custody on Thursday night.
Mr. Szijjarto said Friday that the captain had filed a formal complaint protesting his detention, and a member of his legal team, Balazs M. Toth, told the state news service MTI in a statement that his client denied violating any rules or committing any offenses.
Mr. Toth said the accusations were “premature and not more than a hypothesis at this time,” adding that there was no certainty about what had happened. The captain, he said, had 44 years of experience without any accidents and had been rattled by the events on Wednesday night.
Kang Kyung-wha, South Korea’s foreign minister, met with Mr. Szijjarto in Budapest on Friday, and they viewed the rescue operations at the foot of Margaret Bridge.
“Usually, we express joy when visiting with foreign ministers,” Mr. Szijjarto said. “Unfortunately, today’s visit is no cause for joy.”
Nighttime Danube cruises have become a top tourist draw in Budapest in recent years. The river was harnessed into a controlled bed in the 19th century and has not caused major flooding damage to the city. But the Danube’s swift currents, multiple bridges, and busy passenger and freight traffic have made navigating on the waterway difficult.
Mabeusz, an association of travel companies in Hungary, offered condolences in a statement on Thursday. The association said that “Danube cruises in Budapest are absolutely safe” and that “cruise companies follow all the water transportation rules and regulations.” There has not been an accident on the Danube in Budapest with a similar toll in recent memory.
The deadliest recent accident on the Danube was the collision of a passenger boat with a freighter in southern Romania that claimed more than 200 lives in 1989, according to Folyamihajo, a specialist shipping website in Hungary.