VANCOUVER, British Columbia - At least five people died after a whale watching boat with 27 people on board sank off Vancouver Island and a rescue mission remained active late Sunday, Canadian authorities said.

The vessel made a mayday call late Sunday afternoon on what was a clear and sunny day in the tourist community that is a popular destination for whale watchers on Canada's West Coast, the Joint Rescue Coordination Centre said.

Royal Canadian Navy and Canadian Armed Forces Public Affairs Officer Melissa Kia confirmed to CBS News that at approximately 5 p.m. local time a tour boat from a local company, the Leviathan II, sank off the coast of Tofino, British Columbia, with 27 people on board.
Desmond James, Lt Commander with Joint Rescue Coordination Center in Victoria, British Columbia, told CBS News that five people were confirmed dead, 21 had been rescued and one person was still missing.

James told CBS Radio the vessel was partially submerged eight nautical miles north west of Tofino. Over the phone he said he was not sure if anyone was wearing life jackets. He said there was one helicopter and several boats, using lights, trying to keep up the search.

Valerie Wilson, a spokeswoman for the Vancouver Island Health Authority, said 18 people were taken to a Tofino hospital from the boat. She said of those, three were transferred to other hospitals and some had already been discharged. She added that others could be discharged throughout the evening.

Coast Guard vessels and search and rescue aircraft were searching for the missing individual. The helicopter and aircraft being used in the waters off of Tofino had equipment to search in the darkness.

Boats from the nearby Ahoushat First Nation arrived first on the scene, said aboriginal Councilor Tom Campbell. He was on the waterfront and watched as rescue personnel brought several survivors ashore.

"Their looks tell the whole story," he said by phone from Tofino. "You can't describe looks on people that are lost. They look totally lost -- shocked and lost."

Campbell said his cousin pulled at least eight people from the water into a rescue boat.

John Forde, who runs The Whale Centre, another whale watching operation, responded to the call for help and was told the search was for four or five missing people.

"It's a pretty sad situation when you're doing a grid pattern to an area hoping to see something," he said adding that it didn't look hopeful as time dragged on without finding more survivors.

The ship that went down was the 20-meter Leviathan II, operated by Jamie's Whaling Station, Forde said. He said he had no idea how it could've sunk.

"Over the course of a season and years we take out thousands and thousands of people on these trips in conditions similar to today. I have no idea what the issue was or what actually happened," Forde said.

Forde said Jamie's Whaling Station was one of the first of its kind off Vancouver Island and had been around for many years.

It wasn't the first fatality on the whale watching company's record. In 1998 one of its vessels capsized during an excursion, sending four people on board into the water. The operator and a passenger died.

Jenn Hamilton, a spokeswoman for British Columbia Emergency Health Services, said five ambulances were dispatched and several off-duty paramedics went to the dock to help Sunday evening.

Tofino Mayor Josie Osborne tweeted "thoughts & prayers are with passengers, crew, emergency responders & their families."

The Associated Press contributed to this report.