NBA superstar LeBron James has spoken publicly about Kobe Bryant's tragic death, posting a heartfelt tribute to his great friend and idol on social media.

Basketball icon Bryant and his 13-year-old daughter Gianna were killed in a helicopter crash in Calabasas, California, on Monday (AEDT), sparking an outpouring of emotion across the world.

Footage emerged yesterday of James getting off the LA Lakers' team plane on the way back from Philadelphia, wiping away tears and hugging loved ones.

NBA players and celebrities from all walks of life were quick to pay their respects to Bryant and LeBron took to Instagram on Tuesday afternoon to join in, but admitted he struggled to find the right words.

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"I'm Not Ready but here I go. Man I sitting here trying to write something for this post but every time I try I begin crying again just thinking about you, niece Gigi and the friendship/bond/brotherhood we had!" James wrote.

"I literally just heard your voice Sunday morning before I left Philly to head back to LA. Didn't think for one bit in a million years that would be the last conversation we'd have. WTF!! I'm heartbroken and devastated my brother!!

"Man I love you big bro. My heart goes to Vanessa and the kids. I promise you I'll continue your legacy man! You mean so much to us all here especially #LakerNation and it's my responsibility to put this s*** on my back and keep it going!!

"Please give me the strength from the heavens above and watch over me! I got US here! There's so much more I want to say but just can't right now because I can't get through it! Until we meet again my brother!! #Mamba4Life #Gigi4Life."

Earlier, it was revealed James and Bryant spoke on the phone just hours before the helicopter crash. Bryant had called James to congratulate the LA Lakers star on passing him to become the third-highest scorer in NBA history.

On the weekend, Bryant paid tribute to James on social media after his friend surpassed him in the NBA record books during a game in Bryant's hometown of Philadelphia against the 76ers.

"Continuing to move the game forward @KingJames. Much respect my brother," Bryant tweeted.

James and Bryant, widely considered two of the best NBA players of the past 20 years, won gold medals for Team USA at the 2008 and 2012 Olympics.

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After passing Bryant on the list of all-time leading point-scorers on the weekend, James opened up about how Kobe has influenced him.

"The first time I ever met him, he gave me his shoes on All-Star weekend. It's surreal. It doesn't make sense, but the universe just puts things in your life," James said.

"And I guess when you live in the right way, when you just give it everything to whatever you're doing, things happen organically.

"And it's not supposed to make sense, but it just happens. And I'm happy just to be in any conversation with Kobe Bryant, one of the all-time greatest basketball players to ever play, one of the all-time greatest Lakers."