Amy Winehouse's European tour is off to a disastrous start, with the British singer cancelling two appearances after she was booed in Serbia for mumbling her way through songs.

Winehouse, whose career has been derailed by ongoing drug and alcohol abuse, is hoping for a comeback.

But late Saturday, the 27-year-old pop star arrived one hour late to a show in Belgrade. The disappointment continued as she mumbled lyrics, dropped her microphone and stumbled across the stage. She even disappeared at times, leaving the band to play alone.

Winehouse's erratic behaviour left many of the 20,000 concert-goers feeling disappointed, especially in light of the 38-euro ticket price in a country where the average monthly wage is just 300 euros.

"It was horrible," Ivana Bilic told The Associated Press. "She should have cancelled the whole thing, rather than appear at all like this."

On Sunday, a spokesperson for Winehouse said she had cancelled two upcoming shows: a concert in Istanbul scheduled for Monday and a show in Athens set for Wednesday.

Earlier this month, Winehouse reportedly completed an alcohol rehabilitation program at the Priory clinic in south-west London. She then gave a much-praised secret performance in the city.

The singer won five Grammys for her 2006 album Back to Black..

With files from The Associated Press