The Associated Press said the boat went down near Tofino. The AP adds:
"The vessel made a mayday call late Sunday afternoon on what was a clear and sunny day in the tourist community of Tofino, a popular destination for whale watchers on Canada's West Coast, the Joint Rescue Coordination Centre said."
The Leviathan II, owned by Jamie's Whaling Station in Tofino, is 65 feet in length, according to the tour company's website. It is the company's largest boat.
In a statement on the site, owner Jamie Bray said, in part:
"We are doing everything we can to assist our passengers and staff through this difficult time.
"We are cooperating with investigators to determine exactly what happened."
Bray also thanked the rescue teams, including the local First Nation communities. Alec Dick of the Ahousaht First Nation tells Canada's Global News that some local fishermen, spotting a flare, were among the first to respond and helped pull people out of the water.
Tofino Mayor Josie Osborne tweeted a message of support for passengers and crew on Sunday night.
#Tofino's thoughts & prayers are with passengers, crew, emergency responders & their families. Thank you all for your messages of support.