At least five people are dead after a whale watching boat carrying dozens of passengers sank off the coast of Tofino, B.C., Sunday.

A massive search-and-rescue effort was launched after the vessel made a mayday call shortly before 4 p.m., said the Joint Rescue Coordination Centre.

A total of 27 people were on board when the ship capsized.

The JRCC called off the search late Sunday night.

According to officials, 5 people are dead, 21 were rescued and one person remains missing.

The ship belongs to Jamie’s Whaling Station and Adventure Centres, which offers whale watching tours in Tofino and nearby Ucluelet on zodiac-style rigid-hulled inflatable boats, as well as larger 65-foot cruisers.

It is believed the boat that sank is the MV "Leviathan II," a three-deck cruiser that is the largest in the company's fleet.

Witness Chris McLellan said local First Nations people and other whale watching tour boats were the first to respond to the mayday call.

"Everyone just converged when they heard on the radio what was happening," said McLellan, who heard the report over transmission radio.

Ambulances and emergency responders started arriving at the dock around 4 p.m., he added.

“The ambulances -- It was one after another after another,” he said. “They just didn’t stop.”

McLennan said he saw two body bags on the dock.

A spokesperson for EHS said a critical transport unit was sent in to fly two patients to hospital, and other people were being treated on the dock by paramedics.

Some passengers were being treated in private homes in the area, and off-duty paramedics jumped in to help, they added.

Josie Osborne, Tofino’s mayor, sent a message on Twitter thanking people for the outpouring of community support.

“Thoughts and prayers are with passengers, crew, emergency responders and their families,” she wrote.

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