Billy Crystal has paid tribute to his pal and comedy brother Robin Williams at the Emmy Awards, movingly remembering him as "the greatest friend you could ever imagine".

Following the ceremony's in memoriam segment, Billy appeared on stage at Los Angeles' Nokia Theatre to honour Robin, who was found hanged in his Northern California home on August 11. A luminous image of the late comedian hovered overhead.

"He made us laugh, big time," said Billy.

After Robin's apparent suicide, Billy simply wrote on Twitter of his long-time friend and Comic Relief co-host: "No words."

But he found moving words to remember Robin at the Emmys, recalling family gatherings, ball games and nights on stage together.

"I used to think if I could put a saddle on him and stay on him for eight seconds, I was going to do OK," said Billy.

"It's very hard to talk about him in the past because he was so present in all of our lives. He was the brightest star in the comedy galaxy."

Billy concluded by reflecting on the eternal glow Robin would continue to give, long after he was gone.

"And you'll think to yourself, 'Robin Williams, what a concept'," he said.