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The sister of Boston Celtics point guard Isaiah Thomas was killed in a single-car accident Saturday morning in Federal Way, Washington.

According to the News Tribune's Craig Sailor, Chyna J. Thomas, 22, was pronounced dead at the scene of the accident after the 1998 Toyota Camry careened into a barrier after the car drifted into the shoulder.

"That vaulted the vehicle head-on into the sign post," State Patrol spokesman Trooper Nick King said, per Sailor.

According to Washington State Patrol, Thomas was not wearing a seat belt at the time of the accident.

"We are terribly saddened by the tragic loss of Chyna Thomas," the Celtics said in a statement Saturday, according to ESPN.com's Chris Forsberg. "The thoughts and prayers of the entire Celtics organization are with Isaiah and his family."

NBA commissioner Adam Silver also released a statement expressing his condolences:

Thomas and the Celtics are scheduled to open their first-round playoff series against the Chicago Bulls on Sunday at 6:30 p.m. ET at TD Garden.

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Adam Himmelsbach of the Boston Globe reported members of Thomas' inner circle will head to Boston on Sunday morning to be with the point guard.