The smoke has caused emergency room visits to spike and potentially thousands of deaths among the elderly and infirm.

The blaze, dubbed the Glass Fire, broke out before dawn near Calistoga and raced toward the adjacent towns of Deer Park and St. Helena, with flames advancing to within a mile of the Adventist Health St. Helena hospital.

As wildfire smoke from the west makes its way across the continent, lung health experts say cloth and dust masks won't filter out dangerous particles.

Firefighters trying to contain the massive wildfires in Oregon, California and Washington state are constantly on the verge of exhaustion as they try to save suburban houses, including some in their own neighborhoods.

The same smoke that painted California skies orange also helped crews corral the state's deadliest blaze of the year by blocking the sun, reducing temperatures and raising humidity.

About one hundred wildfires have burned an area nearly as large as the state of New Jersey across the U.S. West, creating smoke that gave California, Oregon and Washington state the worst air quality levels in the world.

Oregon officials haven't released an exact death count for the wildfires but at least four fatalities have been reported in the state.

At least three people were killed in Oregon fires and a small child died in blazes in Washington state, while hundreds of homes have been lost.

Flames racing through dry brush destroyed at least four homes and forced more than 1,000 people to flee a northern California lake community.