The 14-year-old was riding westbound on Howells Road near Manatuck Boulevard when he attempted to cross the street and was struck by a westbound 2011 Honda CRV at 10:25 a.m., according to police.
The vehicle, driven by 36-year-old Nube Cajamarca of Bay Shore, remained on the scene. Cajamarca was not injured, police said.
The teen, who lives in Brightwaters, was transported to Good Samaritan University Hospital in West Islip with serious injuries, authorities added.
The Honda was impounded for a safety check as the investigation continues.
Anyone with information about the crash is asked to contact the Suffolk County Police Third Squad at 631-854-8352.
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