Other eyewitnesses told celebrity news site TMZ they heard the helicopter’s engine sputtering before it went down.
The LA County Sheriff’s Department shared pictures from the scene of the accident, showing a fire truck and smoke emerging from the hills.
The National Transportation Safety Board identified the crashed helicopter as a Sikorsky S-76B and said it was sending a team to investigate the crash.
Police have asked people to stay away from the crash site in order not to interfere with the investigation.
Why was Kobe Bryant so famous?
Bryant played his entire 20-year career with the Los Angeles Lakers. He retired in April 2016.
His achievements include being the 2008 NBA Most Valuable Player (MVP) and two-time NBA Finals MVP. He was also NBA scoring champion twice and a two-time Olympic champion.
He famously scored 81 points against the Toronto Raptors in 2006, the second-highest single-game total in NBA history.
He also won an Oscar for best short animated film in 2018 for Dear Basketball, a five-minute film based on a love letter to the sport he had written in 2015.
Bryant and his wife, Vanessa, have three other daughters, Natalia, Bianca and Capri.
Bryant was accused of sexual assault in 2003 by a 19-year-old woman working at a Colorado resort. He denied the allegation, saying the two had consensual sex. The case was dropped after the accuser refused to testify in court.
He later apologised, saying he recognised that “she did not and does not view this incident the same way I did.” A subsequent civil suit was settled out of court.
What has the reaction been?
Tributes for the sports star poured in on social media following news of the crash.
Shaquille O’Neal, who played alongside Bryant at the Lakers between 1996 and 2004, said there were “no words to express the pain I’m going through”.
“I love you and you will be missed,” he wrote on Instagram alongside a photo of the pair in their Lakers kits.
Deron Williams, who won an Olympic gold alongside Bryant, said he was lost for words. He described Bryant as “the greatest competitor I have ever gone up against and played with.”
Former basketball player Tony Parker said he was “heartbroken”.
“Terrible news,” tweeted US President Donald Trump.
“He loved his family so much, and had such strong passion for the future. The loss of his beautiful daughter, Gianna, makes this moment even more devastating.”
Former US President Barack Obama described Bryant as “a legend on the court” and said he was “just getting started in what would have been just as meaningful a second act”.
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Eight-time Olympic gold medallist sprinter Usain Bolt said he could not believe the news.
Rapper Kanye West tweeted his appreciation for “the life you’ve lived and all the inspiration you gave”.