His 13-year-old daughter Gianna was also killed in the crash near Calabasas, California, a source told the Associated Press. Los Angeles County Sheriff Alex Villanueva said in a press conference Sunday that seven other people are also believed to be dead.
The Federal Aviation Administration said an S-76 helicopter went down under unknown circumstances. Authorities are investigating the cause.
Bryant lived south of Los Angeles in coastal Orange County for much of his adult life, and he often used helicopters to save time and avoid Southern California's notorious traffic. Even as a player, he often traveled to practices and games by helicopter, and he kept up the practice after retirement as he attended to his business ventures.
Bryant was married to Vanessa Bryant, and the couple had three other daughters in addition to Gianna.
Villanueva said his office would not confirm the identity of the victims until the coroner does, saying Sunday it is "extremely disrespectful" for the families to learn about the deaths through TMZ. The crash happened around 9:47 a.m. Pacific time, he said.
Bryant played his entire 20-year career with the Los Angeles Lakers and won five NBA titles. He is fourth on the NBA's all-time scoring leader list.
When he retired, he told Fox News contributors Jim Gray that he wants to be remembered that "I was blessed with talent, but that I worked as if I had none."
"Nooooooooooo God please No!" tweeted former Miami Heat star Dwayne Wade.
Bryant had one of the greatest careers in recent NBA history and became one of the game’s most popular players as the face of the 16-time NBA champion Lakers franchise. He was the league MVP in 2008 and a two-time NBA scoring champion, and he earned 12 selections to the NBA's All-Defensive teams.
"There's no words to express the pain Im going through with this tragedy of loosing my neice Gigi & my brother @kobebryant," Bryant's former teammate Shaquille O'Neal tweeted. "I love u and u will be missed. My condolences goes out to the Bryant family and the families of the other passengers on board. IM SICK RIGHT NOW."
"He will be remembered most for inspiring people around the world to pick up a basketball and compete to the very best of their ability," NBA Commissioner Adam Silver said in a statement. "He was generous with the wisdom he acquired and saw it as his mission to share it with future generations of players, taking special delight in passing down his love of the game to Gianna."
President Trump called the news "terrible."
Former President Barack Obama called Bryant a "legend."
The Associated Press contributed to this report.