Keith Urban dedicates song to Nicole Kidman

Nicole Kidman and Keith Urban attend the Celebrate Life Ball at Grand Hyatt Melbourne. Photo / Getty Images

Keith Urban has put paid to rumours of a split from wife Nicole Kidman, dedicating a song to her at his Sydney concert and telling the audience he loves her.

He also told his fans at the Saturday night gig Kidman was there watching.

"About this time eight years ago we were about five days away from getting married. And maybe a few weeks before that, my fiancee and I were talking about getting married and she said she was worried," Urban told the Allphones Arena audience.

Urban said he understood the fact she was worried because it was such a huge commitment.

"I tried to reassure her that I was born to be her man ... the only thing I could do was reassure her, comfort her, be strong," he said, explaining that he decided to write a song to reassure her.

"I wrote this song for my wife and she's here tonight ... she is an extraordinarily pure and beautiful light. I love you baby," he said, before singing his hit, Once In A Lifetime.

Urban had a few other surprises up his sleeve inviting Australian singers Jimmy Barnes and Jessica Mauboy up on stage for renditions of Cold Chisel's When the War is Over and AC/DC's It's A Long Way To The Top.

Mauboy came on first, dressed in a flowing, grey and white maxi dress before Barnesy made his appearance. Urban was generous, allowing Barnesy to steal the limelight with his impressive vocals, particularly on the infamous AC/DC song.

Proving that the concert should actually have been billed "Keith Urban, and friends" the singer invited another artist on stage a few songs later.

A verse into the Oasis hit, Wonderwall, Joel Madden, a coach on the Nine Network's The Voice, came on stage to sing the rest of the song.

Madden looked the epitome of cool in shades and a denim shirt and the two men embraced at the end of the song.

"The next guest is Elvis Presley," Urban joked after Madden left the stage.

Urban played over two hours worth of his own hits for the responsive Sydney crowd.

He also made his way through the audience at various stages, inviting a 12-year-old girl up on stage with a sign and giving away his guitar to a girl in the crowd after he had signed it.

For the encore, he played some songs on his own with an acoustic guitar before inviting his band back for a high-octane finish.

"It feels so good to be back, thanks Sydney," he said.