Two people, including a police officer, have been killed in a shooting on the Virginia Tech university campus, scene of America's worst gun massacre four years ago.
The gunman remains on the loose.
A news release from the university said the police officer was shot after pulling someone over for a routine traffic stop.
Witnesses told police the gunman ran towards a car park on campus. A second person was later found dead there.
Virginia State Police will be taking over the investigation, according to the news release.
The university locked down the campus after the shooting.
"The campus community should continue to shelter in place and visitors should not come to campus," the school said.
The suspect was described as a white male wearing grey tracksuit bottoms, a grey hat with neon green brim, a maroon hoodie and a backpack.
"It's crazy that someone would go and do something like that with all the stuff that happened in 2007," said Corey Smith, a 19-year-old who was heading to a dining hall near the site of one of the shootings, but stayed inside after seeing the alerts from the school.
"It's just weird to think about why someone would do something like this when the school's had so many problems."
Harry White, 20, a junior physics major, told The Associated Press in a phone interview that he was queueing for a sandwich at a Subway restaurant in a campus building when he received a text message alert about the shooting.
He said he did not panic, thinking instead about a false alarm about a possible gunman which caused the campus to be locked down in August. He used an indoor walkway to go to a computer lab in an adjacent building, where he checked news reports.
"I decided to just check to see how serious it was. I saw it's actually someone shooting someone, not something false, something that looks like a gun," he said.
Mr White said the campus was quieter than usual because classes ended yesterday and students are preparing for the start of exams.
He said he did not see anyone outside from the windows of the computer lab after he received the alert. But he also did not detect any signs of panic.
The shooting came on the same day as Virginia Tech, which has about 30,000 students, was appealing against a $55,000(£35,200) fine by the US Education Department in connection with the university's response to the 2007 rampage, when a student gunman killed 32 students and staff and then shot himself.
A report of a possible gunman at Virginia Tech on August 4 set off the longest, most extensive lockdown and search on campus since the 2007 bloodbath led the university to overhaul its emergency procedures.
No gunman was found, and the school gave the all-clear about five hours after sirens began wailing and students and staff members started receiving warnings by phone, email and text message to lock themselves indoors. Alerts were also posted on the university's website and Twitter accounts.
That incident marked the first time the entire campus had been locked down since the 2007 shooting, and the second major test of Virginia Tech's improved emergency alert system. The system was revamped to add the use of text messages and other means besides email of warning students.
The system was also put to the test in 2008, when an exploding nail gun cartridge was mistaken for gunfire. But only one dorm was locked down during that emergency, and it reopened two hours later.