A man was killed Friday afternoon when the motorcycle he was driving hit the curb on Tustin Street in Orange and crashed into a tree, police said.
No other vehicle appeared to be involved in the fatal crash, which occurred about 4 p.m. on northbound Tustin Street near Santa Ana Canyon Road, according to Orange police.
The driver was pronounced dead at the scene. His identity has not been released.
That section of Tustin Street was closed for several hours after the crash.
Authorities said it was not known whether the motorcyclist was under the influence or was riding at a high speed. The accident remains under investigation.