A rare whirlwind struck an outdoor concert site today in Venice, Italy, forcing the cancellation of tonight's show by Seattle rock band Pearl Jam.

More than 20 people were injured, according to the concert organizer's Web site and Italian news sources, after eight temporary towers containing lights and speakers collapsed in the wind. Part of the stage also was damaged and trees were downed in the San Giuliano park in Mestre, a mainland area of Venice where the music festival was being held; the historic heart of the city was not affected.

More than 20,000 concert-goers were already at the site for the Heineken Jammin' Festival and were evacuated. Thousands more fans were diverted and concerts were cancelled throughout the weekend. It was to be the only Italian appearance of Pearl Jam, which is on a European tour this month.