VENICE, Italy — A towering, out-of-control cruise ship rammed into a dock and a tourist river boat on a busy Venice canal on Sunday morning, injuring four tourists and sparking new calls for placing restrictions on cruise ships in the famed but strained tourist city.

The collision happened about 8:30 a.m. on the Giudecca Canal, a major thoroughfare that leads to St. Mark’s Square in the northeastern Italian city.

The cruise ship, apparently unable to stop, blared its horn as it slammed into the much smaller river boat and the dock as dozens of people ran away in panic.

Now this is terrifying. Venice. Cruise ship. The two don’t go together. #Venice #CruiseShip pic.twitter.com/QVoN0TNi3m

— WALDEMAR JANUSZCZAK (@JANUSZCZAK) June 2, 2019

Medical authorities say four female tourists – an American, a New Zealander and two Australians between the ages of 67 and 72 – were injured falling or trying to run away when the cruise ship rammed into the tourist boat, the River Countess.

The cruise ship’s owner, MSC Cruises, said the ship, the MSC Opera, was about to dock at a passenger terminal in Venice when it had a mechanical problem. Two tugboats guiding the cruise ship into Venice tried to stop the massive cruise ship, but they were unable to prevent it from ramming into the river boat.

“The two tugboats tried to stop the giant and then a tow cable broke, cut by the collision with the river boat,” Davide Calderan, president of a tugboat association in Venice, told the Italian news agency ANSA.

Calderan said the cruise ship’s engine was locked when the captain called for help.

Italian officials said the Venice collision underscored the need to ban cruise ships from using the busy Giudecca Canal, but they stopped short of calling for a ban on cruise ships.

“Today’s accident in the port of Venice proves that cruise ships shouldn’t be allowed to pass down the Giudecca anymore,” said Danilo Toninelli, Italy’s transport minister. “After many years of inertia, we are finally close to a solution to protect both the lagoon and tourism.”

The MSC Opera was built in 2004. It can carry over 2,675 passengers in 1,071 cabins. According to its sailing schedule, it left Venice on May 26 and travelled to Kotor, Montenegro, and Mykonos, Santorini and Corfu in Greece before returning Sunday to Venice.