A Bronx man was killed and a teenage girl riding with him was seriously hurt in a motorcycle accident Wednesday night in Upper Nyack, police said.

Niky Ortiz-Castillo, 27, was driving south on Route 9W just before 8:30 p.m., about a half-mile south of Brittany Court, when his 2009 Yamaha crossed to the other side of the road and struck a guardrail, Clarkstown police Sgt. Jo Anne Fratianni said Thursday.

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Ortiz-Castillo and his passenger, Miguelena Padilla, 16, also of the Bronx, were thrown from the motorcycle, resulting in serious injuries, police said. Both were brought to Nyack Hospital, where Ortiz-Castillo was later pronounced dead.

Padilla was transferred to New York-Presbyterian/Columbia University Medical Center and was in critical condition, police said.

Both victims were unconscious after the crash and unable to speak to investigators, Fratianni said. The cause of the crash remains under investigation.

Both Ortiz-Castillo and Padilla were wearing helmets.

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Route 9W was temporarily closed between Christian Herald Road and Brittany Court while Clarkstown police worked the scene.