A whale-watching tour boat struck a humpback whale that surfaced without warning off the coast of Victoria Monday, sending two passengers to hospital with undisclosed injuries.

Prince of Whales Whale Watching said one of its smaller zodiac vessels was in an area near Race Rocks Ecological Reserve watching another humpback right before it happened at 2:45 p.m.

“After about three minutes of the vessel transiting away from the animal that was spotted, the vessel struck what was thought to be a humpback whale,” said Ben Duthie, operations manager for the tour company. “That animal had not been previously observed, and happened to surface immediately in front of the vessel.”

Duthie said the boat was travelling between 24 and 28 knots, equivalent to a speed of about 44 to 52 kilometres per hour in a car, and launched off the whale.

“The front of the bow went airborne and came down. Two of the passengers moved to the side and were injured,” said Duthie. “The severity of the injuries have not been disclosed at this point.”

The vessel returned to the Victoria harbour, where paramedics transported the injured passengers to hospital.

The company confirmed that one of the passengers has since been released, while the other remained in care Tuesday.

He said the captain of the boat suffered a minor ankle injury and was a bit shaken up, but he’s doing okay physically and mentally.

Duthie called it an “unpredicted, isolated incident” because the whale was not observed in the area before it surfaced, and said it was the first time it’s happened to one of the company’s tour boats in 22 years of operation.

“We feel very extremely sad for everybody that was involved and we take this incident very seriously. The safety of our passengers and our crews is our number one priority,” he said.

While growth in the humpback whale population that traverses B.C.’s coast is encouraging, some experts say they’re also seeing an increase in the number of related boat strikes.

“Unfortunately [they’re] more common than most people think. We definitely have reports of larger whales being hit by cruise ships, by freighter ships, tanker ships coming into Vancouver,” said Dr. Martin Haulena, head veterinarian for the Vancouver Aquarium. “It definitely happens and it can definitely be serious for the whales as well as people.”

Whales can suffer blunt force trauma from boat strikes, and Haulena said that can make it difficult to assess their injuries after one occurs.

“Sometimes it can be an injury that doesn’t really manifest itself for a few days,” he said. “It might not be immediately clear that there was any damage to the whale.”

The Department of Fisheries and Oceans told CTV News it was aware of the incident and an initial investigation has determined that the whale was unhurt in the collision.

The DFO said it’s now determining whether it will investigate possible animal endangerment.

The Transportation Safety Board said it was also aware of the incident and that it is gathering information to determine if an investigation will be required.

Duthie said Prince of Whales is also conducting its own internal investigation as a learning tool for the future, though it appears the captain was strictly abiding by all whale-watching guidelines.

With files from CTV Vancouver Island's Scott Cunningham