Four people have died in a plane crash southeast of Sioux Lookout, the Royal Canadian Air Force (RCAF) confirmed on Sunday.

A specialized Ontario Provincial Police unit was sent to investigate the cause of the crash and identify the four deceased, who were located on board, OPP spokesperson Allison Lawrence told CBC News.

"We've only been able to identify two of the four, and we're still working on notification [of their families] for those two. Until we have [identities for] all four, we are not going to be able to release the names of the victims," Lawrence said on Sunday afternoon.

The plane was privately owned by the pilot, Lawrence said.

Rescue crews found the aircraft early Saturday, according to Joint Rescue Coordination Centre Trenton. There were no survivors among those on board.

"Our thoughts are with the families and loved ones of those onboard in this difficult time," David Lavallee, spokesperson for 1 Canadian Air Division and Canadian NORAD Region Headquarters, said in an email on Sunday. 

JRCC Trenton organized a search on Saturday after the plane was reported to be overdue for arrival. The plane was a Piper PA-28 Cherokee, which is a two- to four-passenger light plane used for family, flight training or taxi, and it was in transit between the two northwestern Ontario towns of Dryden and Marathon.

Lavallee said the search involved two RCAF aircraft, specifically, a CC-130H Hercules from the Winnipeg-based 435 Squadron and CH-146 Griffon helicopter from the 424 Squadron, based at 8 Wing Trenton, Ont.

An Ontario government helicopter also helped in the search, and Civil Air Search and Rescue Thunder Bay provided support.

Searchers used the aircraft's emergency locator beacon to find the plane, Lavallee added.

Sioux Lookout is a town about 350 kilometres northwest of Thunder Bay. 

The Sioux Lookout detachment of the OPP is now investigating the fatal airplane crash, according to a news release issued Sunday morning.

The Transportation Safety Board of Canada has also been notified, a spokesperson confirmed to CBC News, and they are sending a team of investigators to the accident site to gather information and assess what happened.