Budapest, Hungary — As divers descended Friday into the Danube, Hungarian authorities predicted it would take an extended search to find the 21 people still missing after a boat carrying South Korean tourists was rammed by a cruise ship and sank into the Danube river in Budapest. Seven people so far are confirmed dead and seven others were rescued.

Nineteen South Koreans and two Hungarian crew members — the captain and his assistant — remain missing.

Foreign Minister Peter Szijjarto and his South Korean counterpart, Kang Kyung-wha, visited the site and met with rescue and search officials before holding talks.

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Authorities are also expecting help from Serbia, where the Danube flows after leaving Hungary. "It is not unimaginable that we will need to depend on them in the coming days," Szijjarto said.

Divers in full equipment went into Danube but were unable to inspect the wreckage of the boat due to the extremely murky waters and heavy currents from recent rains. Officials said it could take days to recover the 70-year-old boat, which was built in the former Soviet Union.

A diver gets out from the Danube River after a dive to the wreckage of a boat under Margaret Bridge in Budapest, Hungary, Friday, May 31, 2019. Seven people are confirmed dead and seven have been rescued, while 21 people remain missing, Laszlo Balogh / AP

Just hours after Wednesday night's collision, the body of one victim was found nearly 7 1/2 miles downstream from the site of the collision, near the Hungarian capital's parliament building.

"The wreck is located more than six meters (20 feet) deep and the water level continues to rise because of the expected rainfall," Szijjarto added.

Hungarian police have detained and questioned the captain of the Viking Sigyn river cruise ship that collided with a sightseeing boat. Szijjarto said the 64-year-old Ukrainian captain protested being considered a suspect. Identified only as Yuriy C., he is suspected of endangering water transport leading to a deadly mass accident. Police have proposed placing him under arrest.

The Viking Sigyn has been allowed to sail onto Germany but Kang said the ship's owner "has promised to fully cooperate with the investigation."

A South Korean group on a package tour of Europe — including 30 tourists, two guides and a photographer — were on an hour-long sightseeing tour of Budapest when their boat collided with a Viking cruise ship during a downpour Wednesday evening.

Survivors say they were lucky to grab onto a drifting lifeboat Wednesday evening while looking in horror as others around them struggled in the dark, rainy waters, shouting for help.

The South Korean government said no one was wearing a life jacket.

Video released by Hungarian police showed the sightseeing boat, identified as the Hableany (Mermaid), traveling closely side-by-side and in the same direction as the German-built Viking cruise ship as they approached the Margit Bridge.

The Hableany then appears to steer slightly to its left, into the path of the 135-meter (443-feet) long cruise ship, which continued to sail on at the same speed. The two collided and the sightseeing boat then tipped over on its side between the bridge's two supports.

Police Col. Adrian Pal said it was unclear what caused the Hableany to steer into the path of the Viking.