(CNN) Hours after explosions rocked a Texas chemical plant outside Houston early Wednesday, officials said there is no way to know how long a fire at the site will burn.

An early morning explosion at the TPC Group plant damaged the small city of Port Neches and injured at least three employees. A series of smaller explosions occurred throughout the day, and a larger one in the afternoon launched a tower into the air with balls of fire, authorities told reporters Wednesday night.

A mandatory evacuation was issued for areas within a 4-mile radius of plant because of the potential for more explosions.

Jefferson County Judge Jeff Branick, who issued the mandatory evacuation, said the initial explosion knocked out power to the plant. Authorities have no "ability to check the volume of available chemicals" and "no way to calculate burn rates" going forward, he said.

At least three tanks were on fire, and emergency response teams were on the plant site working to prevent the blaze from spreading, Troy Monk, director of health safety and security for TPC Group, which operates the Port Neches manufacturing plant about 90 miles east of Houston, told reporters.

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