Simmons paid tribute to his cousin Zachary Simmons, 21, on Sunday morning (AEST), just two days after he was, as expected, selected with the top pick by the Philadelphia 76ers. Melbourne native Ben Simmons tweeted a photo of Zachary and him, taken at the draft in Brooklyn, with the simple hashtag #ripZacharySimmons.

"I'm glad I could share this moment in my life with you. Rest in peace Cuzzo  Much love Zachary Simmons," he also tweeted.

"Hearing the news this morning is a reminder to never forget the important things in life."

CBS reported that American Zachary was killed in the early hours of Saturday morning, US time, after being struck by a black SUV at the intersection of Willow Avenue and Sixth Street in Hoboken.

Zachary's mother, Monique Steele, told CBS the car was going at least 70 miles (112 kilometres) an hour.

"To be speeding enough to kill my child is beyond me," Steele said.

"He had just went (sic) to the NBA draft for his first cousin — No.1 draft pick."

New York's Daily News reported that the impact propelled Zachary Simmons' body into the rear of a parked car and, according to authorities, he was pronounced dead at Jersey City Medical Center at 4:25am.

Hudson County Sheriff Frank Schillari told the publication police were initially looking for a black Cadillac Escalade, but had widened the search to "large black SUVs" such as GMC Yukons and Chevy Tahoes, believed to also have New York licence plates.

"Investigators are analysing pieces of the suspect vehicle and video footage at this time," Schillari said.

Zachary Simmons was reportedly at a friend's birthday party on Friday night in the hours before the hit-and-run.

Ben Simmons had already joined the Sixers in Philadelphia after the draft.

Much of the Simmons family is based in the United States, several in the New York area.