Intensive care paramedics took the man to Canberra Hospital in a serious condition with head and chest injuries just after 5pm, according to the ACT Emergency Services Agency.

But he died shortly after.

Acting station sergeant Stephen Booth said it was too early to say if speed was a factor.

"It's the first fatality for the ACT in 2016," he said.

"ACT Policing's Collision Investigation and Reconstruction Team are examining the circumstances surrounding the collision. A report will be prepared for the Coroner."

Debris from the bike including its seat was strewn along the road verge for about 25 metres from the tree where the bike rested.

Police are yet to release the rider's age.

Cotter Road was closed for several hours while police investigated the crash. Drivers were detoured through Uriarra Crossing.

Police asked anyone who saw the crash who has not yet spoken with police to contact Crime Stoppers on 1800 333 000, or at crimestoppers.com.au.