Tributes have been pouring in for renowned author Harper Lee, who has died at the age of 89.

Lee penned one of the world's most enduring classics To Kill A Mockingbird, with a much anticipated follow-up, Go Set A Watchman, published just last year, 55 years after the release of the original.

Lee is believed to have passed away in her home in Alabama, United States at around 4am on Friday morning, February 19.

Tributes have been pouring in on Twitter with fans of the author paying their respects, thanking her for her work and sharing quotes from her novels.

Selma director Ava DuVernay quoted a famous line from To Kill A Mockingbird in her tribute posted on Twitter: "You never really understand a person ... until you climb into his skin and walk around in it. Thank you, #HarperLee."

Erin Brokovich, the woman whose life served as the basis of a film starring Julia Roberts, tweeted that To Kill a Mockingbird "changed her life" and that she hopes to "pay it forward" by writing a book of her own.

Apple CEO Tim Cook also quoted a line from To Kill A Mockingbird on his Twitter account. "Rest in peace, Harper Lee," he posted, adding: "The one thing that doesn't abide by majority rule is a person's conscience."

Buffy The Vampire Slayer star Sarah Michelle Gellar also tweeted a message for the author to "rest in peace".

Actor Matthew Modine, best known for his role in Stanley Kubrick's Full Metal Jacket, tweeted a tribute thanking Lee for creating the world of To Kill A Mockingbird, "Bless you #HarperLee Thank you for the chance to get inside the skin of Atticus. You made us all more conscious."

Lee was also awarded the Presidential Medal of Freedom by George W. Bush

Daryl Hannah, star of the movie Splash and Netflix series Sense8, said: "Thank you Harper Lee for Atticus, Boo Scout & the rest .... Peace."

Journalist Piers Morgan also paid his respects, hailing To Kill A Mockingbird as the "one of the greatest book ever written."

Modern Family star Ariel Winter shared the quote, "People generally see what the look for and hear what they listen for" which is being shared by many fans today, with many others posting the infamous line, "I wanted you to see what real courage is."

One fan described To Kill A Mockingbird as "the most essential novel for a growing mind", while journalist Una Mullally commended Lee on teaching "justice, goodness, fairness for the vulnerable" in her work.