BUDAPEST   -   Rescue workers are searching for 21 people still missing after a boat carrying South Korean tourists capsized on the Danube in central Budapest. Seven people have been confirmed dead and seven were rescued, with the other 21 still unaccounted for.

South Korea’s foreign minister, Kang Kyung-wha, and a team of South Korean divers were expected to land in Hungary on Thursday, and dozens of relatives of those on board were also due to travel to Budapest.

The Mermaid, a sightseeing boat that can take up to 60 passengers, sank in bad weather at about 9pm local time (2200 BST) on Wednesday, after it was hit from behind by a much larger cruise ship. The rescue effort was hampered by driving rain and poor visibility.

Seven people were pulled from the water on Wednesday evening, including one close to a bridge two miles south of where the boat sank. Hungary’s human resources minister, Miklós Kásler, said four of those rescued had been released from hospital, and the other three were in a stable condition. The fast current meant the search was taking place along many miles of the river. There were 33 South Korean passengers and two Hungarian crew members on board when the boat was hit. Video footage suggests the boat sank within seconds.

The Very Good Tour agency, a South Korean firm, said most of the people aboard had been part of an organised tour party, which had set off despite the weather. “Other boats were making tours too and we decided to go on after passengers agreed,” Lee Sang-moo, an agency official, told Associated Press. “Our company humbly accepts all the responsibility that is ours.”

The group had left South Korea on 25 May for a one-week trip that had begun in Munich. The agency said it was flying family members of those affected to Budapest. It said two South Korean guides and a photographer were also on board the boat. The agency said it did not believe anyone on board was wearing a life jacket.

The boat had apparently been returning from an hour-long evening sightseeing tour. Lee named six women and one man, aged between 31 and 66, as the survivors found so far. A six-year-old girl, who was on board with her family, was not listed among the survivors. Hundreds of boats ply the Danube each day in Budapest. Some offer short sightseeing tours and other larger cruise ships dock in the city before continuing along the river. The waterway was busy on Wednesday despite the poor weather.

“Both ships were heading north ... and when they arrived between two pillars of the Margit Bridge, for some reason the Mermaid turned in front of the Viking ship. As the Viking comes into contact with it, it overturns it and in about seven seconds, as it turned on its side, it sank,” said Col Zsolt Gábor Palotai, the head of Budapest’s disaster management office.

The Viking cruise line operator said one of its ships was involved in an incident on the river. No one aboard the ship was injured. The company said it was cooperating with authorities but gave no further details.

Hungary’s prime minister, Viktor Orbán, sent a letter to his South Korean counterpart, Lee Nak-yeon. “Our thoughts and prayers go out to the families of the victims.

 We stand together with the people of South Korea in these most difficult moments,” it said, according to an excerpt posted on Twitter by Orbán’s spokesman. Orbán said Hungarian emergency services were continuing to do everything possible to search for survivors.