The Oregon Department of Environmental Quality on Wednesday issued an air quality advisory for Klamath and Jefferson counties as several large wildfires burn in the state.

Smoke from the Hagelstein and Elk fires in Klamath County and the Cram fire in Jefferson County are causing unhealthy air quality for sensitive groups, according to an agency statement. The advisory is expected to last until at least 10 a.m. Thursday.

The Cram fire is the largest in the state, expanding overnight to more than 64,000 acres, according to the Northwest Interagency Coordination Center. It is zero percent contained, while the Elk fire in Klamath is 39% contained and has burned around 2,700 acres.

Gov. Tina Kotek on Wednesday declared a wildfire state of emergency that will last through the end of the year, citing the already-devasting wildfire season and more hot, dry conditions to come.

This is Oregon’s first air-quality alert due to wildfire smoke this year, said Chris Varley, a department spokesperson. The timing is not unusual compared to recent years, when similar warnings have been issued around mid-July.

But it’s part of a larger trend of wildfire season starting earlier because of climate change, according to data dating back to 2000, Varley said.

Infants and children, people with heart or lung disease, older adults and pregnant people are at most risk of health issues from inhaling smoke, which can irritate eyes and lungs and worsen some medical conditions, the statement said.

The Cram fire is 15 miles east of Madras in Jefferson County and the Elk fire is 7 miles southwest of Beatty in Klamath County.

The department’s air quality index map showed Redmond and Madras each approaching 150 — the high end of the orange section for air “unhealthy for sensitive groups” — on Wednesday afternoon.

The department also expects intermittent smoke in Crook and Deschutes counties.

Winds are forecast to push the smoke further east and the air quality in a given area can change quickly depending on wind and weather, Varley said.

Limiting exposure is the best way to protect yourself from harmful air quality, Varley said.The agency recommended precautions such as staying inside, keeping windows and doors closed and avoiding strenuous outdoor activity. Air filters or purifiers, including a do-it-yourself version using a box fan, also can help.

“Cloth, dust and surgical masks don’t protect from the harmful particles in smoke,” the agency statement said. Certain respirators approved by the National Institute for Occupational Safety and Health can offer protection: Look for a letter N, R or P with the number 95, 99 or 100.

Once air quality improves to moderate or healthy levels — yellow or green on the air quality index — it’s safe to open doors and windows to air buildings out.

Check current conditions on the Oregon Smoke Information Blog, DEQ’s Air Quality Index, or the free OregonAIR app.

— Maddie Khaw covers breaking news, public safety and more for The Oregonian/OregonLive. Reach her at mkhaw@oregonian.com.