The fire occurred at the Free Expression Tunnel, which connects Central and North campuses.
John Barnwell, of the N.C. State Public Safety Department, said two 5-gallon containers of concrete cleaner were on fire and the liquid was seeping into a drainage system.
Barnwell said the concrete cleaner was being used for renovations to the tunnel. Barnwell said the liquid reacted with water, so the fire has to burn out on its own.
While the cause of the fire is not yet known, it is being investigated as arson. The State Bureau of Investigation is investigating the incident, along with campus police.
Authorities said someone did break into a trailer on the construction site. There are no suspects at this time.
Hazmat officials are trying to determine how the liquid will affect the drainage system. There are no reports of any injuries.
Anyone with information about the case is asked to contact campus police at