Search and rescue officials say the plane was travelling from Pentiction to Boundary Bay when it went down around 5 p.m. local time.
Canadian Navy search and rescue spokeswoman Capt. Annie Djiotsa says the Piper twin engine Commanche crashed near Brenda Mines, about 22 kilometres west of Peachland in B.C.'s Okanagan region.
She says a Cormorant helicopter was dispatched to the crash site, which was about 55 kilometres from Pentiction.
Chris Harbord from the B.C. Ambulance Service confirmed three people in critical condition were taken from the crash site to hospitals in Kelowna and Kamloops.
"It took a while for search and rescue to find the plane and when they did we understood there was four patients onboard," she said.
The Transportation Safety Board says it will be investigating the crash and plans to send two officials to the site on Tuesday morning.