The U.S. government said it was providing technical support to California utility regulators working to stem a leak from a natural gas storage facility.

California Gov. Jerry Brown this week declared a state of emergency "given the prolonged and continuing duration of the Aliso Canyon gas leak." The federal government said the state had lead authority over the gas storage facility and efforts to protect public health.

"The U.S. Department of Transportation's Pipeline and Hazardous Materials Safety Administration is working closely with the State of California to provide technical assistance and support to state and local regulatory agencies, including the California Public Utility Commission, related to their response and oversight activities," it said in a statement.

The site near Los Angeles has been leaking since late October. The Southern California Gas Co., which controls the facility, has been unable to control the leak. The state says the leak appears to be the result of damage to well infrastructure located about 500 feet underground.

In its latest incident response update, the state government said a relief well was about 75 percent toward its final target depth of 8,700 feet. Surveys using magnetic ranging were able to locate the 7-inch pipe believed to be leaking natural gas in the form of methane.

Methane is non-toxic, though gas leaking from the site may contain chemicals associated with cancer risks. Methane is more potent than carbon dioxide as a greenhouse gas.

"This leak is already the biggest single source of climate pollution in the state of California, equal to the exhaust of 7 million cars every day," the activist group Greenpeace said.

The utility company is offering reimbursement packages for residents forced to evacuate as a result of the leak. An online video highlights air-purification techniques for residents still in the area.

SoCalGas said it may be February before the leak is stopped.