United States President George W Bush and First Lady Laura on Tuesday joined thousands of grief-struck students and staff of Virginia Tech University at a memorial service in the campus, where 33 people were killed in the worst school shooting rampage in the country.

The gathering was called a convocation or get-together of the students and faculty to mourn the loss of lives on a tragic day, when a gunman killed 32 people before turning the weapon on himself.

"Laura and I have come to Blacksburg today with hearts full of sorrow. This is a day of mourning for the Virginia Tech community, and it is a day of sadness for our entire nation," Bush told a packed auditorium in the campus where the memorial service was held.

"I came here to express sympathy. In this time of anguish, I hope you know that people all over this country are thinking about you," he said.

He said they could find source of strength from within the community. "You have a compassionate community here. This community spirit is a source of strength.

"People who have never met you are praying for you, for your friends. There is real power in this. They are thinking about you asking God to provide comfort to all the affected," he added.

Assuring them that the administration stands by them, Bush said, "You can call anyone of us at any time of need."

The Governor of Virginia Tim Kaine, who rushed back from an official visit to Tokyo, also attended the Convocation at Blacksburg, Virginia.

Kaine said the campus has shown incredible spirit in dealing with the situation. World is watching you in this hour of darkness and you responded incredibly, he added.

Various faith leaders and some families of students also attended the Convocation.

With tears choked in their eyes, students hugged each other as they gathered at the Cassell Coliseum, wearing the orange and maroon uniform amid tight security.