PHILADELPHIA (AP) — A white powder found inside a balloon near the Liberty Bell prompted the evacuation of the area for a few hours Thursday before tests showed it was flour.

The Liberty Bell Center building and National Park Service land around it, including Independence Hall, were evacuated, and part of a street was closed to traffic after a guard found the balloon at the visitors entrance around 2:30 p.m.

Tests later determined the powder was harmless, and officials expected to reopen the area soon, Independence National Historical Park spokeswoman Jane Cowley said shortly before 6:30 p.m.

‘‘The substance was just flour,’’ Cowley said.

Testing on the powder first was done at a lab set up at the scene, FBI spokesman J.J. Klaver said. The powder quickly was found to not be explosive or radioactive, but it was what Klaver called a ‘‘biological substance,’’ which could have been anything from yeast to the deadly animal disease agent anthrax.

Preliminary field tests showed it was flour, Klaver said, but the FBI still wanted to test it further.

The powder was being taken to a state lab. If it’s confirmed to be harmless, the FBI likely would not investigate who left it at the Liberty Bell Center, Klaver said.

Nearby buildings, which include offices and a federal courthouse, were not evacuated Thursday. But some streets were closed to pedestrians.

The Liberty Bell was forged to commemorate the 50-year anniversary of William Penn’s 1701 Charter of Privileges, Pennsylvania’s original Constitution. The bell, with its famous crack, became an icon of American independence when abolitionists adopted it as a symbol of their efforts to end slavery.

On July 8, 1776, the ringing of the Liberty Bell from the Independence Hall tower called people to the first public reading of the Declaration of Independence.