A motorcycle rider died from injuries sustained after losing control and going down on Interstate 680 in Danville on Sunday night, according to the California Highway Patrol.

The motorcyclist -- a man whom investigators were still working to identify -- may have been hit by another vehicle when he was down on the freeway, according to the CHP.

The situation unfolded around 8:10 p.m. Sunday on northbound I-680 just north of the El Cerro Boulevard interchange in Danville, according to the CHP.

Emergency personnel responded to find the male rider of a red 2004 Honda CBR motorcycle dead on the freeway from injuries sustained in a crash, according to the CHP.

The initial investigation indicates the motorcycle lost control and crashed for unknown reasons. Then, an approaching vehicle may have struck the rider while he was down on the freeway, according to the CHP.

That second driver remained at the scene and was fully cooperative with the investigation, the CHP said. Other possible witnesses also remained at the scene to provide statements to investigators.

The cause of the crash is still under CHP investigation.

The Contra Costa County Coroner's Office will release the victim's name publicly once his identity is confirmed and his family notified, according to the CHP.

The fatal collision initially caused all northbound lanes of I-680 through the area to be closed, but the center media and No. 1 lane soon opened to allow traffic to continue through while the investigation carried on, the CHP said.

Investigators ask any witnesses to the crash, or events leading up to it, to contact Contra Costa CHP in Martinez at 925-646-4980.