BUDAPEST, Hungary (AP) — Hungarian police have detained the captain of a cruise ship that collided with a sightseeing boat packed with South Korean tourists, causing it to sink quickly in the Danube River in Budapest, as loved ones of the missing and dead were expected to arrive Friday in Hungary.

Seven people are confirmed dead and seven have been rescued, while 21 people remain missing in the waters.

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.

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

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

Their small sightseeing boat had almost finished its tour and was almost at a stop when the larger cruise ship hit it under a bridge near the riverbank parliament building, a city landmark. They said about 20 people were on the deck taking photographs or preparing to disembark. The others were in the cabin.

"I saw that big cruise ship coming closer to us but I had never imagined it would ram our boat," said a 31-year-old South Korean surnamed Jeong. She was quoted by South Korea's Yonhap news agency.

Jeong said she and others on the deck were thrown into the cold Danube waters by the impact of the collision. Police said it took only seven seconds for the boat to overturn and sink.

She said she saw a lifeboat drifting close by and managed to seize hold of it, also throwing a rope to another tourist surnamed Yoon.

"Our boat was turned over in an instant and began sinking," Yoon, 32, told Yonhap. "All those on the deck fell into water and I think those staying in the cabin on the first floor couldn't probably get out of the ship swiftly."

Rescue crews were looking for the missing people, but operations have been 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.

Meanwhile, crews also prepared to raise the sunken boat. Officials have said it could take days to recover the 70-year-old boat, which was built in the former Soviet Union.

Police, who launched a criminal investigation into the incident, said late Thursday that they had detained and questioned the Ukrainian captain of the larger vessel.

The 64-year-old man is suspected of endangering water transport leading to a deadly mass accident. In line with Hungarian laws, the suspect was identified only as Yuriy C., referencing his first name and the initial letter of his last name. Police proposed the arrest of the Odessa resident, described earlier by police as an experienced sailor.

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Hyung-Jin Kim contributed from Seoul, South Korea.