Seven bodies were pulled out of the Sava River and divers searched for five other missing people Friday after a group of kayakers smashed into a dam being built in southeastern Slovenia, police said.

Police spokesman, Pavel Perc, told reporters that two people managed to swim ashore after their boats broke up and capsized. Both were hospitalized; one was in critical condition, he said.

The accident happened late Thursday, when the group, in two kayaks, apparently hit a dam under construction near Sevnica, a town 56 miles (90 kilometers) southeast of the capital of Ljubljana. The dam, part of a hydroelectric plant, is currently built only to about the height of the water.

Slovenian TV journalist Goran Rovan, who witnessed the accident, told the state-run news agency STA that two canoes capsized and broke apart when they hit the whitewater passing through the dam gates. The occupants fell into the river and were sucked into the underwater tunnel leading to the generator turbines.

Police divers raced immediately to the scene, but rescue operation has been hampered by the river’s strong currents. More than 15 divers combed the river Friday, trying to find survivors or bodies. A police helicopter flew over the area, while police, civil protection and fire services swept the river banks.

Prime Minister Janez Jansa rushed to the site in early Friday, declaring the accident a “great tragedy.”

“(Rescuers) are doing everything that is humanely possible,” he said.

Slovenian TV said the occupants of two other boats _ a part of a four-boat excursion _ left the river before reaching the site where the plant is being built.

The trip was dubbed “The Final Descent,” STA said, as it was to be the last ride down that section of the river, which will soon be blocked by the hydroelectric plant.

Slovenian media said a local mayor, who also is a member of parliament, was among the victims.