Washington, April 23 (DPA) Thirty-two white balloons were released into the air at Virginia Polytechnic Institute Monday morning, as classes resumed one week after the university suffered the worst massacre in US history.

A bell tolled 32 times - once for each victim - on Drillfield at the heart of the university campus starting at 9.45 a.m., when police first heard reports that South Korean student Cho Seung-Hui had barricaded himself into an academic hall and opened fire in classrooms.

The 32 balloons were released shortly after the bell toll, steps from Norris Hall where the shootings took place. Hundreds of orange and maroon balloons - the university colours - followed as a sign of the campus and world's solidarity.

Students also gathered at West Ambler Johnston Hall across campus, where Cho killed a female student and resident counsellor a full two hours before entering Norris Hall.

Classes resumed Monday for the first time since the shootings, though the university's 27,000 students have been given great leeway in how they want to continue the year - including an offer to have only that work evaluated which was handed in before the shooting.

All students killed last week are to receive posthumous degrees from Virginia Tech.