Bay Area residents who think they're smelling smoke are probably right. Smoke from fires elsewhere in California and Oregon drifted into the Bay Area on Thursday, air quality officials said.

Fires in Nevada and Butte counties are generating smoke that's moving into the Bay Area. Also, smoke from Northern California and Oregon fires is coming down the coast and entering the area through the Golden Gate, according to the Bay Area Air Quality Management District.

"We expect the smoke to last through Saturday and potentially through the weekend," air district spokeswoman Kristine Roselius said.

Some parts of the Bay Area appear to be experiencing more smoke than others. Marin County is experiencing heavy drift smoke from the Northern California fires, and residents will smell smoke, the Marin County Sheriff's Office tweeted.

The Napa County Office of Emergency Services and the Lafayette Police Department both said there are no fires in either area, and the smoke residents are smelling is from the Northern California fires.

San Mateo County is also experiencing quite a bit of drift smoke from fires in Northern California and Oregon, county officials said.

Smoke can irritate the eyes and airways, causing coughing, scratchy throats and irritated sinuses. It can trigger wheezing in people with asthma, emphysema and chronic obstructive pulmonary disease, air quality officials said.

Bay Area residents are advised to limit outdoor activities to avoid unnecessary exposure if they smell smoke, and set air conditioning units and car vent systems to re-circulate to prevent outside air from moving inside, air quality officials said.

Residents can also reduce exposure to smoky air by staying inside with windows and doors closed, if possible, according to the air district. Those who cannot do so should seek out cooling centers in their respective areas.

It's also a good idea to stay tuned to local media for changes in smoke or weather conditions, air quality officials said.