Rescue operations underway on the Danube (photo: Zsolt Szigetváry/MTI).

The boat, which was moored near the Hungarian Parliament, was reportedly hit by another tourist vessel, then turned over on the river, which has been flooding with strong currents while a rainstorm enveloped Budapest.

News portal Index.hu said the boat was carrying 33 mostly South Korean tourists, plus two Hungarian crew. It added that 14 people were rescued safely while another was successfully resuscitated. However, at least three were initially reported dead – rising to seven after a statement from the Ambulance Service at 12.30 a.m. – as search efforts continued into the night for the remaining missing.

Index.hu cited the boat’s owner as confirming that the boat, named Hableány (Mermaid), had sunk. Rescue efforts were under way with more than a dozen vehicles visible several hundred meters downstream from the site of the accident, Reuters reported.

Television footage showed the Danube embankment closed off by police on the Pest side, directly across from the World Heritage site of Buda Castle. Police ordered all shipping to stop on the Danube in central Budapest, Reuters added.

Index.hu reported after midnight that poor visibility, rain and rapid currents caused by high water were hampering further rescue efforts.

Update: As of Thursday morning, the rescuers were still looking for 21 people, according to a report by 24.hu. The number of confirmed deaths climbed to seven. The wreckage of the Hableány was found at 1.30 a.m. on the riverbed near a pillar of Margaret Bridge.

The report adds that the other vessel involved in the crash is a large, 95-room luxury boat called Viking Sigyn. The authorities are currently conducting an investigation aboard the boat.

Index.hu reported later Thursday morning that due to the cold conditions (with the Danube water measured at 10-12 degrees Celsius), participants in the rescue effort see little chance of finding more survivors, and the death toll is thus expected to rise significantly.