Metallica paid tribute to Green Day after replacing them at a festival.

The heavy metal group stepped in for the 'Oh Love' punk band at the Voodoo Festival in New Orleans, after they cancelled all forthcoming dates due to frontman Billie Joe Armstrong's ongoing rehab.

Two songs into their set, Metallica singer James Hetfield told the crowd: ''We! Are! Green Day! - Except a little taller!''

He later added: ''You're hoping Green Day are going to show up, right? So am I. They're getting help. They're getting it sorted out. The world needs them.''

He also dedicated the track 'Battery' to the front man, saying: ''This one's for Billie.''

During their encore, Metallica - which also includes Kirk Hammett, Lars Ulrich and Robert Trujillo - played the opening to Green Day's 'American Idiot', although James cut it short and told the crowd, ''We can't play that song.''

Green Day announced yesterday (29.10.12) they are cancelling all scheduled dates in 2012 and postponing shows they had scheduled for 2013.

Bassist, Mike Dirnt, wrote on the band's website: ''The timing for this isn't ideal, but Billie Joe's well-being is our main concern.

''We are happy to say that Billie Joe is doing well, and we want to thank you all for the outpouring of support and well wishes that we have received, and we can't wait to see you all again soon.''