MOSCOW (AP) — A tour bus carrying Chinese tourists plunged through the ice on Russia’s Lake Baikal, killing eight people, officials said.

One of the Chinese tourists managed to escape from the bus, which was crossing the frozen lake on Friday, Irkutsk regional Gov. Igor Kobzev wrote in a Telegram post on Saturday. He said the dead included seven Chinese tourists and the driver.

The bus plunged into a 3-meter (10-foot) -wide ice crevasse, Russia’s Emergencies Ministry reported. The lake is 18 meters (59 feet) deep at the site of the accident, it said. The ministry said rescuers used underwater cameras before embarking on a diving operation.

The regional prosecutor’s office said a criminal probe had been opened. The Irkutsk tourism office reported on Saturday that the bus tour had been run by an unregistered operator.

Lake Baikal, the world’s deepest freshwater lake, is one of Russia’s key tourism attractions. Numbers of Chinese visitors to the country soared in recent years, after Moscow and Beijing introduced a mutual visa-free regime.

Russia’s Foreign Minister, Sergey Lavrov, sent condolences to his Chinese counterpart, according to an online statement published on Saturday on the ministry’s website.

According to the statement, Lavrov told Wang Yi that Russian authorities “are conducting a full investigation” and expressed hope that the accident “will not negatively impact the positive dynamics of bilateral tourism.”