LOS ANGELES (Reuters) - Governor Jerry Brown on Wednesday declared a Los Angeles-area natural gas leak that has been sickening nearby residents for more than two months an emergency, calling for alternatives to stop the underground leak if existing efforts fail.

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Southern California Gas Co, which operates the well that is the site of the underground methane leak, is trying to stop it by drilling a relief well to reach a damaged pipeline, then injecting fluids and heavy mud into it.

The governor’s office said in a statement the utility will need to identify how it will stop the leak if a relief well fails to seal it - or if the existing leak worsens.

The leak was discovered on Oct. 23 at a well used for natural gas storage in Aliso Canyon just outside Los Angeles’ Porter Ranch neighborhood, which is home to more than 30,000 people. Thousands of residents were forced to move over the holidays, with the company underwriting their temporary housing.

Officials from Southern California Gas, a division of Sempra Energy, say they expect to stop the leak in late February to late March.

The leak, which state officials have said accounted at its peak for a fourth of California’s 20 million metric tons a year in greenhouse gas emissions from methane, is believed to have been caused by a broken injection-well pipe several hundred feet beneath the surface of the 3,600-acre (1,457-hectare) field.

Nearby residents have complained of such ailments as headaches, nausea and respiratory irritation from mercaptans, the odorants added to natural gas, according to Los Angeles County health officials. They have said past studies found no long-term health effects from mercaptans.

The governor’s office said it had taken steps to coordinate the local, state and federal response to the leak, which at last count was releasing more than 30,300 kilograms of methane per hour, and stop it as soon as possible.

“It has become so complex and there are so many different state agencies involved that it needs to be coordinated and directed in an organized way, like for a disaster,” said Kelly Huston, deputy director of the governor’s Office of Emergency Services.

The emergency declaration by Brown, a Democrat, follows calls by local officials in Los Angeles for increased state regulation of gas storage facilities.

The declaration allows the governor’s administration, if necessary, to quickly waive laws in the future to deal with the crisis, said the governor’s spokesman, Evan Westrup.

Residents of Porter Ranch have said they want the gas field shut down.

The governor, who visited Porter Ranch on Monday, in his declaration called for regulators to assess the long-term viability of natural gas storage facilities in California.

“As we have since this incident began, SoCalGas stands willing and ready to cooperate with the governor’s office, all state and local officials and regulatory agencies,” Dennis Arriola, president and chief executive of the company, said in a statement.

The storage field is the second largest such facility in the western United States by capacity.