An uncontrolled leak of natural gas that has persisted for at least 11 days at a ConocoPhillips field in Alaska has cut into oil production at the site, according to state data.

State agencies have provided little information about the response to the leak, the suspected cause, or how much gas has been released since it was first discovered on March 4.

Crude output at ConocoPhillips’ Alpine unit fell to 36,861 barrels on March 13—the last data available—compared with a range of about 51,000 to 58,000 barrels a day in February, before the leak was detected, according to the Alaska Department of Revenue.

ConocoPhillips said it is mobilizing a drill rig in order to "proactively address source mitigation of the surface gas release at Alpine CD1,” according to a company website set up in response to the leak.

The subsurface leak was discovered at CD1, Alpine's oldest drill pad and production site. Three days later, ConocoPhillips evacuated about 300 workers out of caution, it said in a new website devoted to the incident.

About 400 people normally work at the site, which contains a processing facility and worker camp along with producing wells. CD1 well production was stopped after the leak was discovered, ConocoPhillips said on its website. Alpine is one of the main oilfield units on Alaska’s North Slope.

Neither Conoco nor state officials have commented on the size of the leak, but residents and observers are growing more concerned about the situation. The Alaska Department of Environmental Conservation also said 600 gallons of seawater released at CD1. Seawater is injected into some North Slope fields to boost oil recovery.

No leaked gas has been detected beyond CD1, and no people or wildlife have been harmed, the company said.

ConocoPhillips has begun what it said would be regular briefings with the community of Nuiqsut, an Inupiat village of nearly 500 people located about 8 miles (13 km) from the site.

The gas leak comes just as federal officials have launched a new court-mandated environmental impact statement for ConocoPhillips’ planned Willow development west of Alpine. Willow could produce 160,000 barrels per day, according to ConocoPhillips.

The project has been stuck in the courts after a federal judge in August overturned Trump-era approvals, finding fault with the administration's environmental analysis.

This leak is a warning against further development, said Suzanne Bostrom, an attorney with the Anchorage-based environmental law firm Trustees for Alaska.

“This illustrates exactly the kind of problem that could be expected with Willow,” she said.