Shawn Mathieson

Shawn Mathieson died in the crash. An 18-year-old man suffered serious injuries. (Supplied)

A full-time Ottawa firefighter is dead and another man was seriously injured after a crash in rural southeast Ottawa on Thursday.

The crash happened on a trail near Forced and Russell roads at about 11:50 a.m., according to Ottawa paramedics.

Shawn Mathieson died at the scene.

"It is with sad and heavy hearts that we are confirming the death of an off duty Ottawa firefighter," said Ottawa Fire Services spokeswoman Danielle Cardinal.

Mathieson has three children, sources told CBC. He was born in 1967.

Co-workers offered counselling

He got his start in firefighting at Station 73, just minutes away from the crash site. Firefighters were first to arrive at the scene and began CPR, then realized one of the victims was a firefighter they worked with.

At six feet two inches tall and about 250 pounds, his colleagues affectionately nicknamed him Shrek.

"He was a fun-loving guy," said Peter Kennedy, the president of the Ottawa Professional Firefighters Association, on Friday. "Firefighters are a really close family. So it's like losing one of your own. It's an extended family. We're all very close and we all have great memories."

Grief and trauma counsellors are being made available to his co-workers.

Ottawa snowmobiling crash Navan Roland and Cathy Lanthier March 3 2016

Roland and Cathy Lanthier, seen here snowmobiling on trails not far from the crash site, say it can be dangerous when snowmobilers take curves too quickly. (CBC News)

An 18-year-old man was taken to hospital in critical condition, but his condition improved to serious en route to hospital, paramedics said.

Roland and Cathy Lanthier, who have been snowmobiling for more than 30 years, said trails can be dangerous when snowmobilers take curves too quickly.

"If you meet a guy at the same time in the curve, and they drive too fast, they can't keep on their side," Roland Lanthier said.

Police are investigating the crash.