BUDAPEST, Hungary (AP) — Rescue workers scoured the Danube River in downtown Budapest Thursday for 21 people missing after a sightseeing boat carrying South Korean tourists sank in a matter of seconds after colliding with a larger cruise ship during an evening downpour.

Seven people are confirmed dead and seven were rescued, all of them South Koreans, Hungarian officials said. Police launched a criminal investigation into the incident.

The South Korea-based Very Good Tour agency, which organized the trip, said the boat — a 70-year-old vessel built in the former Soviet Union — had been on its way back after an hour-long night tour on Wednesday evening when the accident happened.

Nineteen South Koreans and two Hungarian crew members — the captain and his assistant — are missing. The tour party had consisted of 30 tourists, two guides and a photographer on a package tour of Europe. Pal Gyorfi, spokesman for the National Ambulance Service, said those rescued were hospitalized in stable condition.

The sunken boat was located early Thursday near the Margit Bridge, not far from the neo-Gothic Parliament building on the riverbank.

Video displayed by Hungarian police showed the sightseeing boat, identified as the Hableany (Mermaid), traveling closely side by side and in the same direction as the Viking cruise ship as they approached the bridge Wednesday night.

The Hableany then appeared to steer slightly to its left, into the path of the cruise ship, which continued to sail on at the same speed. The two collided and the sightseeing boat was then seen tipping on its side between the bridge’s two supports.

“As the Viking comes into contact with (the Hableany), it overturns it and in about seven seconds, as it turn on its side, it sinks,” Police Col. Adrian Pal said.

Pal said it’s unclear what caused the Hableany to steer into the path of the Viking. He said several people aboard the Hableany fell into the water after the collision. The South Korean government said none of those on board was wearing a life jacket.

Police said rescue operations were hampered by the rain and the fast flow of the rising Danube. The search for the 21 missing extended far downstream, even into Serbia, where the Danube goes after leaving Hungary.

Budapest’s Disaster Management Office Chief Col Zsolt Gabor Palotai said the Hungarian army is setting up a pontoon near the capsized ship’s wreck and divers will go into the Danube from there.

Police have questioned the Ukrainian captain of the Viking, but no details have been released. Authorities said both vessels’ captains are experienced, with many years of service with their companies.