Almost two dozen people, most thought be British tourists, were injured when a speedboat hit a water fountain near the town of Harstad, local media reported.
Police said 24 people, including three crew, were on board the two boats, 22 of whom have been taken to hospital.
The British group were on a tour with a local travel agent, a company co-owned by a member of the local police in Harstad and a former employee of the force, police said.
Neither was aboard the boat that hit the fountain but both witnessed the accident.
Norwegian Police said two are thought to have been seriously injured.
The incident is thought to have happened at around 3pm local time (2pm GMT) when a rigid-inflatable boat (Rib) collided with a fountain in the harbour.
None of the injuries are thought to be life-threatening.
Another boat following behind is understood to have been caught up in the accident, and a number of those aboard both boats were thrown into the sea.