Authorities in California ordered the evacuation of nearly 40,000 residents on Friday following a leak from a chemical storage tank that could trigger an explosion and release toxic fumes over a densely populated area.

The tank reportedly contains 26,000 liters of methyl methacrylate, a volatile and highly flammable liquid commonly used in plastic manufacturing.

Fire officials warned that the situation appears serious and could result in major chemical contamination or even an explosion if not quickly contained.

A fire department official said current conditions “look bad,” amid fears that toxic vapors could spread into nearby residential communities.