RIP @Wee_ Oscar one of the nicest and strongest fighting kids I'll ever come across. So sad, really is.
He captured the hearts of everyone, but sadly little Oscar Knox lost his battle to cancer. Sleep tight little man.
Heartbreaking news about Oscar Knox. The attitude and strength of him and his family was inspirational. Rest in peace.
Very sad news. Deepest sympathies to the Knox family
There are none so deserving of appreciation and respect than those parents who have to give a child back to God. Thank you for sharing with us the inspiration that was your precious little boy.
DUP councillor Christopher Stalford
No parent should ever have to bury their child. My thoughts and prayers are with the family of Oscar Knox who was such a brave wee boy.
Deputy First Minister Martin McGuinness
Oscar was a little warrior who faced down sickness and setbacks and showed all of us how precious life is.
Very sad news that Wee Oscar has passed away. A truly inspirational little boy who showed extreme bravery in his short life. Sleep tight wee man.
RIP wee man. You fought the good fight and we'll never forget you. You are hero in all our eyes.
Broadcaster Adrian Logan
Wee Oscar but only in name. A giant who inspired us all. RIP. My prayers are with mummy and daddy and all the family. Love and God Bless.
Celtic footballer Kris Commons
@Wee_Oscar will never be forgotten. A true inspiration. RIP little man.
Linfield footballer Matthew Tipton
Hearing the sad news about Oscar Knox puts everything into perspective.
Such sad news about Oscar Knox. God has yet gained another precious little angel. Sleep tight Oscar, you'll never walk alone!
Rip little Oscar Knox! A wee fighter the whole way, such a shame. Sleep tight wee man.
Just heard @Wee_Oscar has passed away. Horrible news! You were a true wee fighter. God bless you wee man.
Republic of Ireland footballer James McClean
Devastating news about wee Oscar Knox, thoughts and prayers with his family, put up a brave fight. RIP
Cliftonville footballer George McMullan
Terribly sorry to hear about young Oscar, a true legend of a kid. Honoured to have met him.
Cool FM DJ Pete Snodden
Thinking of @Wee_Oscar, such sad news. My thoughts are with his family. His smile and fighting attitude will live with me forever! RIP
Oscar Knox gave us all hope with his strength and attitude to life! RIP
Broadcaster Holly Hamilton
Heartbreaking news this morning... such a brave wee man... RIP Oscar.
Absolutely heartbreaking to hear about Oscar Knox. RIP wee man, your bravery and strength was incredible.
Rip @Wee_Oscar – such a brave brave boy and an inspiration to all!
Ex-footballer John Hartson
My sincere condolences go out to wee Oscar Knox and his family. God love him. He fought his little sox off, truly sad. #godblessoscar
Oscar Knox RIP. What a brave little guy.
Heart goes out to the Knox family, devastating news about Wee Oscar. A fighter to the end.
RIP Oscar Knox. An inspiration to everyone, shine bright wee man.
Heaven's newest angel will shine bright forever.
Wee Oscar left his mark in the world and made people come together and fight against something rather than each other
Cancer is a terrible, terrible thing. The fighting wee Oscar done at five years of age is unbelievable. You'll never walk alone.
Poor Wee Oscar. Wee angel. Xx
Belfast Lord Mayor Máirtín Ó Muilleoir
Devastated to hear of death of #Fearless Oscar Knox, Belfast's most-loved boy. Condolences to Stephen and Leona.
Devastated to hear about @Wee_Oscar. What a hero
RIP Oscar Knox, you were a wee fighter. Heaven truly has gained an angel
Such sad news about Oscar Knox. He is a super human for what he went through. True hero at age of five.
Celtic manager Neil Lennon
This is a very young boy who had such an influence on a lot of people, particularly here within Celtic and the support.
RIP Oscar, heaven has truly gained an angel
GAA pundit Joe Brolly
Such a shame about Oscar Knox. The epic battle to keep one small child alive showed us mankind at its very best.
Heaven is a little brighter today with this smiling wee face! In God's arms little man!
Sad to hear about anybody passing away but to lose your life at the age of five is far too young.
Just reading about Oscar Knox makes me wanna cry, so sad when cancer takes someone so young.
RIP Oscar Knox, such sad news, thoughts are with your family, you'll never walk alone kid.
The world's lost a brave wee legend. We'll never forget you kid.
Donations to raise money for the Northern Ireland Children's Hospice in memory of Oscar can be made via a dedicated JustGiving page at justgiving.com/oscarknox.
In 2011 Oscar Knox (5), from Mallusk, was diagnosed with high-risk neuroblastoma, which affects one in every 100,000 children. He also has the chromosome disorder Jacobsen syndrome, which is thought to affect only 250 children worldwide.
Oscar has received more than 30 blood transfusions and almost 140 platelet transfusions in the past 26 months. Oscar's parents Stephen and Leona run a blog and fundraising campaign, The Wee Oscar Knox Appeal. Around 140,000 people follow Oscar on Facebook and Twitter @Wee_Oscar