Ordinary people are being credited with helping to find and rescue the survivors of a deadly catamaran sinking off the coast of Vancouver Island over the weekend.

The Canadian Coast Guard said two vessels of opportunity rushed to help following a mayday call from the 8.5-metre fishing boat, which started taking on water north of Tofino on Sunday afternoon.

Emergency crews dispatched a lifeboat within minutes of receiving the call, but by the time it arrived all five occupants had already been plucked from the water.

Sadly, despite the combined efforts of Good Samaritans and first responders, the sinking still ended in tragedy.

"Two individuals had cardiac issues and they were reported as deceased when they arrived back in Tofino," Coast Guard spokesperson Dan Bate told CTV News.

The names of the victims haven't been confirmed, but the RCMP said they're both men, ages 32 and 42, and are both from Alberta.

The three survivors were treated in hospital and released.

The catamaran went down near Bartlett Island, very near to the area where the Leviathan II whale watching vessel capsized in 2015, killing six of the people on board.

Tofino Mayor Josie Osborne said the weekend's disaster has sent familiar shockwaves through the remote island community.

But despite the tragic loss of life, Osborne applauded the efforts of everyone involved in the rescue, from first responders to civilians.

"It's a small community and word travels incredibly fast here," she said. "Everybody just steps up and does what needs to be done. Their response is incredibly professional, very caring, very compassionate."

Atleo Air also responded to the sinking, sending a float plane and helicopter into the skies immediately to help pinpoint the location of the fishing boat.

Operations manager Jason Bertin said it's not uncommon for civilians to pitch in when disaster strikes.

"Tofino is a community that lives on the water, and all of us live and work on the water," he told CTV News. "The captain of that vessel was one of us, and if anybody else was in that situation, he would be out look too."

The name of the fishing vessel hasn't been released, and authorities are still working to determine what caused it to sink. The Transportation Safety Board confirmed it has launched an investigation into what happened.

With files from CTV Vancouver's Nafeesa Karim and The Canadian Press