Air quality plummeted as the Pickett Fire spread across California.

A local health emergency was declared in Napa County as the wildfire, which began on August 21, continued to burn and pose a threat to public safety.

County Public Health Officer Christine Wu signed the proclamation in response to what officials described as 'imminent environmental threats to safe water supplies and hazardous waste and materials' caused by the fire.

The Bay Area Air Quality Management District extended its advisory through Wednesday, warning that smoke from the fire was likely to continue affecting Napa, Solano, and Sonoma counties.

Officials said wildfire smoke poses health risks even with short-term exposure, urging residents to remain indoors with windows and doors closed until conditions improve.

Although air quality was impacted, pollution levels were not expected to surpass the national 24-hour health standard, and no Spare the Air Alert was issued.

As of August 27, the fire was 25 per cent contained, with 6,803 acres burned.

The cause of the wildfire remains under investigation.