Mr Alagiah, an award-winning journalist who presented BBC News At Six for the past 20 years, died on Monday from bowel cancer after being first diagnosed in 2014.
Clive Myrie, who earlier this month was honoured to become the University of Bolton’s Pro Chancellor, led a series of emotional tributes.
He said: “On a personal note, George touched all of us here in the newsroom with his kindness and generosity, his warmth and good humour.”
He added: “We loved him here at BBC News and I loved him as a mentor, colleague and friend.
“His spirit, strength and courage in the later years of his life is something his family can be so proud of.
“Journalism has lost a giant.”
Tributes were also paid by Naga Munchetty, Natasha Kaplinsky, Fiona Bruce and BBC director general Tim Davie.
Mr Davie said: “Across the BBC, we are all incredibly sad to hear the news about George. We are thinking of his family at this time.
“George was one of the best and bravest journalists of his generation who reported fearlessly from across the world as well as presenting the news flawlessly.
“He was more than just an outstanding journalist, audiences could sense his kindness, empathy and wonderful humanity.
“He was loved by all, and we will miss him enormously.”
Naga Munchetty was another to become audibly upset as she interrupted her live show on BBC Radio 5 Live around midday to deliver the news.
She said: “Apologies for the emotion in my voice, he was so loved in our newsroom.”
Throughout his career, Mr Alagiah interviewed central political figures, among them former South African president Nelson Mandela, Archbishop Desmond Tutu, and ex-Zimbabwean leader Robert Mugabe.
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He was nominated for a Bafta in 1994 for his coverage of Saddam Hussein’s genocidal campaign against the Kurds of northern Iraq and was named Amnesty International’s journalist of the year in 1994 for reporting on the civil war in Burundi.
He first began hosting the 6pm news bulletin in early 2003, but stepped up to front it solo four years later following the departure of his co-host, Natasha Kaplinsky.
Writing on Instagram Ms Kaplinsky said it was a “privilege” to be friends with the departed broadcasting legend.
She said: “Goodbye dearest George. I will miss you so very much.
“It was such a privilege to be your friend.”