California Governor Gavin Newsom (D) declared a state of emergency on Saturday evening as experts warned that the chemical tank that is overheating in Orange County could explode.

40,000 residents in Orange County, California, were evacuated on Friday amid a chemical leak at an aerospace facility.

On Thursday, a valve overheated on a 34,000-gallon tank used to make plastics.

Authorities said the tank, located in Garden Grove, could either explode or spill thousands of gallons of toxic chemicals.

Several evacuation centers were opened; however, many residents are still refusing to leave their homes.

On Friday evening, Orange County Fire Authority Division Chief and Unified Incident Commander Craig Covey said the temperature of the tank had come down.

"It's down to a temperature around 61 degrees, with 50 being its happy place," Craig Covey said.

However, Covey walked back his statement on Saturday and said drones were measuring the temperature outside of the tank.

As of Saturday, the tank's internal temperature is around 100 degrees, up from 77 degrees on Friday.

On Sunday, TJ McGovern, the Interim Fire Chief for the Orange County Fire Authority, said firefighters discovered a crack in the tank late Saturday night, which could be relieving some of the pressure.

Newsom declared a state of emergency.

"I'm proclaiming a state of emergency in Orange County as California continues to respond to the hazardous chemical incident in Garden Grove," Newsom said.