Media playback is unsupported on your device Media caption School spokesman Larry Hincker says the alert was issued out of ''an abundance of caution''

A lockdown has been lifted at Virginia Tech - site of America's worst school shooting four years ago - several hours following a report of a gunman.

Police scoured the campus after three children said that they had seen an armed man.

The university withdrew the alert on its website and said police would stay on campus for the rest of the day.

Virginia Tech was fined in March this year for not reacting quickly enough to the April 2007 massacre.

Thirty-two people died when a 23-year-old South Korean, Seung-Hui Cho, went on a gun rampage before turning the weapon on himself.

"The campus alert is lifted," the university said at 14:41 (18:41GMT) on Thursday. "There will continue to be a large police presence on campus today.

"Police have not received nor discovered additional information about a person possibly carrying a weapon beyond that reported this morning."

Three children earlier said they had seen a white male holding what "may have been a handgun", walking fast in the direction of campus volleyball courts.

An updated statement on the university's website later on Thursday said that based on the information provided by the children, "we couldn't rule out that this wasn't credible".

"We felt like there was no other option than to issue a campus alert and ask our people to remain secured indoors," the statement said.

The alert issued at 09:37 (13:37GMT) said: "Person with a gun reported near Dietrick. Stay inside. Secure doors."

Police from Virginia Tech and the towns of Blacksburg and Christiansburg searched the campus, but no other witnesses reported seeing the man or anything suspicious.

Authorities said they will continue searching school buildings and facilities.

Most of the university's 30,000 students were on summer break, but there were still a few thousand students and staff on campus when the warning was issued.