A 16-year-old Portland boy was seriously injured after he crashed his motorcycle Sunday evening, police said.

Officers responded to the crash at the intersection of Brighton Avenue and Raymond Road in Portland just after 6 p.m. and found bystanders helping the teen. Police said he was driving east on Brighton, when for “an unknown reason,” he left the road and hit a tree.

The teen was brought to Maine Medical Center with serious injuries. The cause of the crash is unknown, authorities said.

Portland police have not filed any charges in the crash, which remains under investigation.

Authorities ask anyone with information to call 207-874-8532 or 207-874-8575.