Seven South Korean tourists have died and another crowd of 21 people are missing after a boat sank on the Danube river in Hungary's capital, Budapest.
Thirty South Korean tourists and three tour guides, as well as two Hungarian crew, were on the tour boat when it collided with another vessel.
The incident occurred just after 19:00 GMT on Wednesday.
Seven people have been rescued, and a massive search operation is continuing on a river swollen by heavy rainfall.
The rain had led to strong currents on the Danube. Rescue teams say there is little hope of finding more survivors.
A criminal investigation has been launched.
The boat that sank near the parliament building in central Budapest was identified as the Hableany, or Mermaid.
The Hableany has two decks and a capacity of 45 people for sightseeing trips.
CCTV footage has emerged purportedly showing the Hableany and a larger vessel colliding near the Margit (Margaret) Bridge.
Some reports suggest that the Hableany was hit from behind.
This has not been confirmed by the authorities, as they investigate a rare incident on the Danube where navigation is busy but generally safe.
At a news conference on Thursday, police spokesman Adrian Pal said the boat had sunk "within seven seconds" after the collision.
Rescue teams have located the wreckage, and are now preparing to lift the wreckage.
Meanwhile, Imre Horvath, the head of the Hungarian National Shipping Association, said he believed it was a human error, MTI news agency reported, although he gave no further details.
South Korea's foreign ministry confirmed that seven of its citizens had died and 19 were missing.
Hungarian police officials later said 21 people were unaccounted for, but it was unclear whether this included any tour guides and crew members
The South Korean ministry said a team of officials would be sent to Hungary, adding that counselling would be made available to victims' families.
Lee Sang-moo, a spokesman for the tour organiser, told reporters in the South Korean capital, Seoul, that at least one child was among the missing.
Pal Gyorfi, a spokesman for Hungarian emergency services, said seven survivors had been taken to hospital with "hypothermia and shock symptoms".
The rescue effort continued throughout the night and into Thursday, with boats, divers, spotlights, and radar scanning along the river several kilometres downstream.
Emergency crews discovered the wreckage of the Mermaid on the riverbed near the Margaret Bridge.
Rescue teams warned that, as more time passed, the strong currents would carry people further downstream, lessening the chances of finding survivors.
Boat traffic has been halted on the Danube south of Budapest, Reuters news agency reported.
The BBC's Laura Bicker in Seoul says Wednesday's sinking is a painful reminder of the Sewol disaster in 2014.
The ferry of that name sank off South Korea's Jindo island, killing 304 people, almost all of them schoolchildren on a trip.
The sinking was blamed on a combination of illegal redesigns, cargo overloading, the inexperience of the crew, and lax government regulations.