A 6-year-old girl died on Sunday morning after being struck by a car on Blank Lane in Water Mill. The child, Tess Burstein, was declared dead at Stony Brook University Hospital, where she had been rushed by ambulance after first being taken to Southampton Hospital. According to Southampton Detective Sgt. Lisa Costa, Tess’s condition was initially thought to have stabilized, but she regressed. The detective would not specify the nature of her injuries other than to describe them as “trauma.” The driver of the Toyota Prius that struck the girl, Maurice Wittenberg, a 76-year-old Water Mill neighbor, was not ticketed. Mr. Wittenberg had one passenger in the car, his wife, Harriet Wittenberg. Neither was injured. Police impounded the Toyota for a safety inspection, as is routine in accidents involving fatalities. “We have done a preliminary investigation,” Detective Costa said yesterday. “It appears to be accidental in nature.” The accident occurred at about 10:50 a.m., she said. The child’s parents, Annabel Vered and Josef Burstein, live on Blank Lane and in Manhattan. “It is very sad. It has affected the entire community,” the detective said.