As many as 200 people were in Thomson Hall at the time of the incident, which was reported to campus police at about 1:53 p.m. No injuries were reported and the building was deemed safe for people to return just before 3:30 p.m.

The Communications Building next door was evacuated as well for a short time as a precaution, said university spokesman Vince Stricherz.

People in Thomson Hall at the center of campus told campus police that tiles on the second floor popped loose, Stricherz said. Evacuees had some trouble with the doors, he added.

"Somewhere on the second floor, the floor buckled," Roseth said minutes after the building was evacuated.

Thomson Hall, which was built in 1948, houses the Henry M. Jackson School of International Studies. Roseth described it as a collegiate gothic building, with four stories above the ground, plus a basement.

University structural engineers were investigating why the floor buckled, Roseth said.