The University of Texas at Austin campus has been deemed safe after all buildings were evacuated because of a bomb threat.
A male caller said Friday morning that several bombs had been planted on UT's 350-acre campus.
UT President William Powers said in a news conference Friday afternoon that all buildings had been searched and cleared and that, "from a variety of sources, we are very confident our campus is safe."
The threat to the campus was received at about 8:35 a.m. Friday morning when a man with a Middle Eastern accent who claimed he was with al-Qaida said he placed bombs in multiple buildings on campus that would detonate in 90 minutes.
Powers said the university has a protocol to deal with threats and that one part of that protocol is to evaluate the credibility of the situation. Over the next hour, officials investigated the threat and ultimately determined it was prudent to clear all buildings out of an abundance of caution.
The university then posted the following message to its website and to its Twitter account, @UTAustin, at 9:53 a.m.: "Evacuation due to threats on campus. Immediately evacuate ALL buildings and get as far away as possible. More information to come."
Tara Doolittle, UT assistant director media, said alerts were sent at 9:35 a.m. to begin the evacuation.
Powers added that ordering buildings to be evacuated 15 minutes before a bomb threat was to be executed left ample time for students to get to safety and that everyone was safe about 10 minutes after the order had been given.
The campus emptied at quick but orderly paces Friday morning, though students acknowledged an air of confusion about what was going on. The threats coming as violent protests outside U.S. embassies in the Middle East also stirred nervous tension among some students, and UT officials acknowledged global events were taken into account.
"My first thought was that it was a tornado siren because we hadn't gotten any warnings, text messages or anything about it being a drill, so [I thought], 'Oh, it's a tornado,'" said Lauren Saurette, a UT junior from Frisco. "But then 30 seconds later, I got a text saying to evacuate, so obviously it wasn't a tornado at that point."
"I got the text message, and I heard the sirens going off," said Zoe Mirtsching, a sophomore from Dallas. "And at first, I didn't realize they were the loud sirens -- I thought they were just a police siren. And then I read my text message and knew that something was going on, but we didn't know it was a bomb threat at first."
Ashley Moran, a freshman from Houston, said she was waiting to get into class when word quickly began spreading among students to leave immediately. She described the evacuation as "orderly but tense." Another student, Priyanka Patel, told NBC 5 that texts were delayed and calls from mobile phones were failing on the network around campus.
As thousands of people fled the campus, police blocked off roads as lines and lines of cars sat in gridlock trying to leave.
The main campus has 24,000 faculty and an enrollment of 51,000 students that represent every state in the Union and 100 countries.
At 10:27 a.m., the school tweeted the following: "Buildings being checked/cleared. Stay away from buildings. No decision on afternoon classes/activities. Next update at 10:45am."
At 10:45 a.m., UT tweeted the following message: "Time specified in phone threat has passed but we have not yet cleared all buildings. Decision to resume operations&classes will come shortly."
At 11:25 a.m.,UT tweeted the following message: "The University is still under emergency conditions. Please remain away from buildings. As additional information becomes available it will be updated on this site."
At 11:38 a.m., UT tweeted the following message: "All activities except classes will resume at 5 p.m. Buildings may be reentered at noon. Today's classes are cancelled."
The FBI is investigating the phone call. Agents say a hoax is a costly disruption that will come with heavy charges.
"We are working very closely with city, state and federal authorities. We know a great deal of detail about the nature of this phone call. We are very confident that this campus is safe," Powers said.
There were no injuries reported in connection with the evacuation.
The threat to UT was the first of three threats received by college campuses on Friday. North Dakota State University in Fargo received a phone call about a "threat of an explosive device" more than an hour later, and Hiram College in northeast Ohio received an emailed bomb threat late Friday afternoon.
NBC 5's Omar Villafranca contributed to this report.