A hazardous materials leak in Southern California forced the evacuation of more than 44,000 residents Friday as conditions worsened and emergency officials warned of a possible explosion.

The Orange County Fire Authority (OCFA) said the leak was reported Thursday in the city of Garden Grove, 40 miles (64.4 kilometers) southeast of Los Angeles. It has continued to worsen in the last 24 hours, with emergency crews fearing an explosion or thousands of gallons of toxic materials being released into the environment.

"It fails or it blows up," OCFA Division Chief Craig Covey told reporters.

Emergency officials said the 34,000-gallon (128,704-liter) tank contains methyl methacrylate, a toxic and highly flammable liquid chemical used in the manufacture of acrylic plastics. Authorities said the tank system failed after the chemical overheated and caused the tank to start leaking vapors into the air. The compromised tank is located next to two other chemical storage tanks.

"The tank that is in the biggest crisis is in fact unable to be secured and mitigated," said Covey.

"There are literally two options left," he said. "One, the tank fails and spills a total of about 6,000 to 7,000 gallons of very bad chemicals into the parking lot in that area, or two, the tank goes into a thermal runaway and blows up, affecting the tanks that are around them that have fuel or the chemicals in them as well."

Authorities urged residents to heed the evacuation warnings and remain out of the area due to the possible spill or explosion. Officials said air quality was being actively monitored, and all readings were still within "healthy limits."

"It is a highly toxic substance," OCFA Division Chief Nick Freeman told a news conference. "It's extremely flammable, and in its current state, very reactive, and can cause that explosion."

OCFA officials said crews are prepared for the possibility of the chemical spilling out of the tank, with "containment barriers" put in place to prevent the material from entering storm drains, river channels or reaching the ocean.

They added that a spill is the "best case scenario, believe it or not," favorable to an explosion and possible plume of toxic material spreading over the area.

Emergency officials said it was unclear what caused the material in the tank to overheat.

No injuries were reported as of Friday. (AA)