The steps necessary to stop the gas leak from Aliso Canyon in California is underway, though work won't be done until the end of February, a gas company said.

California Gov. Jerry Brown declared a state of emergency "given the prolonged and continuing duration of the Aliso Canyon gas leak" in early January. The site near Los Angeles has been leaking since late October.

Methane is leaking from the site and other gases associated with the mix may contain chemicals associated with cancer risks. Methane is more potent than carbon dioxide as a greenhouse gas. According to advocacy group Greenpeace, the site is leaking the equivalent of the exhaust from 7 million cars every day.

Southern California Gas Co., which controls the site, said workers are operating around the clock to drill the relief well that should stem the leak, though it may be until late February before work is completed.

"We have developed various contingency plans in case we encounter unexpected developments in the relief well drilling process that could slow our current progress," Jimmie Cho, a vice president in charge of safety operations, said in a statement. "Our current schedule to control and stop the leak in February is consistent with the plan we have submitted to [state regulators]."

Once the final target is reached, crews will pour cement into the well to stop the leak at its source.

While residents remaining in the area may experience symptoms of exposure like nausea and shortness of breath, the company said air monitoring data indicate there are no long-term health effects associated with exposure to area gases.

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.