A 58-year-old bicyclist died Saturday morning after he was struck by a semi-truck near Hilo, Hawaii County police said.

The crash happened about 8:45 a.m. on Mamalahoa Highway between Hau Lane and Pukihae Street, just north of Hilo.

Witnesses reported the cyclist hit the sidewalk curb and fell over, then was struck by the truck, said Sgt. Christopher Gali of the police department’s Traffic Enforcement Unit. The cyclist and truck were both traveling toward Hilo.

The cyclist died at the scene. The truck’s driver, a 66-year-old Hilo man, was not hurt.

Police opened a first-degree negligent homicide investigation.

Police closed Mamalahoa Highway in both directions for about four hours while they investigated the accident scene.