Aussie music fans got a treat on Friday when two of the biggest bands in the country put on a free concert.

Wolfmother put on a show for about a thousand people in Sydney in the afternoon at the inaugural Take 40 Live gig.

The show, which was filmed for a TV special, saw them play old favourites like Woman and Mind's Eye, as well as New Moon Rising off their latest album Cosmic Egg.

Front man Andrew Stockdale said the new material had been going down well with fans.

"Cosmic Egg - it seems like you can play that within all the songs from the first record and people just go with it," he told AAP.

"It's a good feeling."

Powderfinger played three "viral" concerts in Brisbane, Sydney and Melbourne across the day.

They kicked off the cross-country concerts with 1,400 fans turning out to see them in Brisbane on Friday morning.

The band played an acoustic set and through Twitter, the morning commute and word of mouth, the crowd gathered in Post Office Square, opposite Brisbane's GPO.

"Good for the soul," said Maxine, a public servant.

"What a way to go to work."

Fans, city workers and bemused police officers were amongst the early morning crowd.

Bass guitarist John Collins told AAP some "some Twittering" had pulled the large crowd.

"It was a chance to play some new songs, have some fun," he said.

"We're going to Sydney to see what happens, we might be doing the same thing somewhere there."

The band has invited other artists to join them as they conduct their mystery tour.

"Come down for a jam phil jameson, you know you cant resist.... dz," one Tweet said, calling on the lead singer of Grinspoon to join the band for their next jam session.

Universal Music's Sarah Chin told AAP the band did not want to have any formal publicity for the surprise sessions apart from using Twitter.