PORTLAND, Ore. — Thick, hazardous smoke could continue to smother the West Coast for days, hindering firefighters battling dozens of deadly blazes that continue to scorch the region.

While a brief, long-awaited rain arrived along the Oregon coast on Tuesday, clearing up the skies in some parts of the state, officials warned that dangerous smoke will remain in the air through at least Thursday.

The Oregon Department of Environmental Quality has extended an air-quality advisory through noon Thursday, as several cities in the state reached their highest-ever-recorded air-quality index ratings during the past week. The state already has seen a significant increase in emergency room visits for smoke-related respiratory conditions.

Sarah Present, a deputy tri-county health officer for the Portland metro region, warned residents in a video message on Tuesday that they should stay indoors.

“This air can worsen asthma or COPD,” she said. “It can lead to heart attacks, irregular heart rhythms and even death.”

“It is so bad that you can likely smell it inside your house, and in some areas, the air quality is so hazardous it is off the charts of the EPA’s rating scale,” she said. “What this means is you should not go outside.”

The smoke that the wildfires in the American West has sent skyward has traveled across the country, causing a milky-orange haze and a dimmed sun as far east as D.C. The smoke, carried along by the jet stream, will linger on the East Coast through at least Thursday, promising surreal skies. Effects on the ground are expected to be minimal.

Here in Oregon, the unusual wildfires have displaced tens of thousands of residents and have left at least eight people dead and at about 16 people missing. There have been approximately 25 deaths in California.

Lower temperatures and higher humidity have allowed the more than 8,600 firefighters to make progress on the 30 large wildfires spreading across nearly 1.7 million acres in Oregon and Washington state, fire officials said Tuesday. Some of those fires continued to grow, while at least one, the Almeda Fire that ravaged communities in southern Oregon, reached 100 percent containment, a rare victory in what has been an alarmingly busy fire season at its outset.

“We now find ourselves one week into this, and without question our state has been pushed to its limits,” Gov. Kate Brown (D) said during a news conference Monday. “As we look toward the next few days, my firefighting teams tell me they are optimistic that cooler weather coming toward the end of this week will be a tremendous help.”

In California, more than 16,600 firefighters continued to face off against 25 major wildfires across the state. The blazes in California have burned more than 3.2 million acres and destroyed more than 4,200 structures, according to state fire authorities.

A cooling trend in California has helped fire crews in the state, but gusty winds have allowed fires to pick up in the north and along the Sierra, said Daniel Berlant, assistant deputy director of Cal Fire. Those wind gusts are expected to continue through at least Thursday.

More than 1,145 homes have been destroyed in Oregon, and 3,185 residents remained in shelters provided by the Red Cross as of Tuesday. Many more are displaced from their homes and waiting for evacuation orders to lift.

While officials on Monday had said 10 people were reported dead in Oregon, the state medical examiner later determined that two of those fatalities were unrelated to the fires, bringing the death toll down to eight. The two subtractions were identified as animal remains.

On Tuesday, the state began consolidating its efforts to identify and report fatalities in a single mobile morgue, the state’s Office of Emergency Management said.

About one-tenth of an inch of rain fell along the Oregon coast on Tuesday, bringing substantial improvements in visibility there, said Daniel Hartsock, a meteorologist with the National Weather Service in Portland. Still, satellite imagery showed smoke lingering over the Willamette Valley and Columbia River Gorge, with smoke moving north from the fires in California. Forecasts predict the first “big rain” will arrive in the valley by Thursday afternoon, Hartsock said.

But Doug Grafe, chief of fire protection at the Oregon Department of Forestry, said the rain could come with some lightning and thunderstorms in the east, which could ignite additional fires.

Livingston reported from Washington.