Columbine High School in Colorado has closed to mark the eighth anniversary of a massacre by two teenage students - days after the Virginia Tech shootings.
The Virginia Tech killings rekindled painful memories of Columbine
In the 1999 attack, Dylan Klebold and Eric Harris shot dead 12 classmates and a teacher before killing themselves.
On Monday, student Cho Seung-hui, 23, went on a gun rampage at Virginia Tech university campus, killing 32 people.
Colorado's governor asked residents to join in a moment of silence for the Virginia Tech victims.
"We experienced a terrible tragedy at Columbine High School," Bill Ritter said.
"The people of Colorado will stand in solemn silence on the anniversary of that dreadful day with the people of Virginia as they grieve."
The BBC's David Willis says it has been a difficult week for the relatives of those who died at Columbine with events at Virginia Tech rekindling painful memories.
Their distress was deepened by a video message from Cho, referring to Harris and Klebold as martyrs.
The shooting at Columbine High School in Littleton remains the worst US high school attack.
Although the school is closing for the day, the authorities do not intend to mark the anniversary with a special ceremony.
The Columbine killers were referred to in Cho's video message
Principal Frank DeAngelis said watching the events at Virginia Tech unfold had proved deeply disturbing for many of the relatives, causing them to relive the pain and horror the tragedy had inflicted.
Following the Columbine killing, a study of school shootings by US investigators concluded that killers such as Klebold and Harris did not just snap - instead they acquired weapons and carefully planned their attacks.
Like Cho, Klebold and Harris killed themselves before the authorities could stop them.
Police refused to release videos and audiotapes made by the Columbine pair amid fears they could spark copycat killings.