Ice broke off a glacier and hit a ship of British tourists sightseeing off a set of remote Arctic islands, injuring 18 people, police and the tour operator said Thursday.

Four people, two with serious injuries, were flown to a hospital on the Norwegian mainland after the accident Wednesday night on the Alexey Maryshev, a Russian research vessel converted into a luxury tour boat, said Jan Tommervold, a deputy sheriff on the Svalbard Islands.

He said the other 14 injured people were taken to a local hospital.

The islands are about 620 miles from the North Pole and about 310 miles north of the Norwegian mainland. They are a popular tourist destination during the summer, with about 20 ships cruising the region.

According to police, the ship had sailed close to the towering Horn glacier for a better look when ice broke off and hit the vessel's side and deck, where some passengers had gathered.

Sheriff's deputy Petter Braathen said blocks of ice also crashed into the water near the ship. The vessel was tossed around and "the passengers were thrown around on the ship," he said.

Some of the passengers were injured by the falling ice, others by the turbulence, officials said.

The 216-foot ship returned to port under its own power and was awaiting a possible investigation, Tommervold said.

Braathen said the ship had sailed unusually close to the glacier.

Ko de Korte of Oceanwide Expeditions, the Dutch Company that operates the ship, said by telephone from the Netherlands that there were 72 people aboard, including 50 British passengers and 22 crew and staff.

"The company director is on his way (to Svalbard)," he said. "We have been operating since 1982 and this is our first accident ... so this is serious."

The Alexey Maryshev was built in Finland in 1990 as a research vessel for the Hydrographic Institute of St. Petersburg and is under long-term contract with Oceanwide Expeditions.